Glossary

This list of terms is both a useful reference, and a fun way of browsing through the terminology in order to learn more about plant species, plant breeding and agricultural techniques.

The original text was adapted from The Amateur Plant Breeder's Handbook by Dr. Raoul A. Robinson. A free download of the handbook is available from www.sharebooks.ca.

As with any page in the Open Breeding Wiki, these glossary listings can be edited by anyone. If you notice any terms that still need to be added, or definitions that can be expanded, please sign up for an account and help make this resource even better.

Glossary: A

Abaca: See: Musa textilis.
Abelmoschus esculentus: Okra, previously called Hibiscus esculentus. This is an annual crop grown for its fruits that are cooked and eaten as a green vegetable. There has been considerable hybridisation with wild species and there is much genetic variation. Scope for amateur breeders working with horizontal resistance.
Abscission: The discarding of plant organs, such as leaves of deciduous trees in the autumn.
Acaricide: See: Miticide.
Acidity: See: pH.
Acre: A measure of land area. One acre is 4840 square yards, or 0.405 hectare.
Acropetal: Growing upwards so that the oldest parts are at the base and the youngest at the tip.
Adlay: See: Coix lachryma-jobi.
Adult plant resistance: Horizontal resistance in many crops, particularly the cereals, is often expressed more in mature plants, and less in young seedlings. This is to be expected because the epidemic intensifies as the growing season progresses. For this reason, horizontal resistance is often called adult plant resistance and, by implication, it is more difficult to observe it, measure it, or screen for it, in young plants.
Aerobic: Living conditions in which there is a plentiful supply of oxygen. Organisms which require oxygen are labelled as aerobic organisms, or aerobes. The converse, meaning without oxygen, is anaerobic.
Aestivation: An organism’s survival of a hot dry summer.
Aflatoxin: Toxins produced by Aspergillus flavus and related fungi. Mouldy feedstuffs contaminated with aflatoxins have caused severe disease and mortalities in livestock, particularly poultry.
African millet: See: Eleusine coracana.
Agaric: Any member of the Agaricaceae, a fungus family in which the fruiting bodies are mushroom shaped.
Agave sisalana: Sisal. Once an important bast fibre crop in its centre of origin in Mexico, and also in East Africa (Kenya and Tanzania), sisal has been largely supplanted by synthetic fibres. Seed set in sisal is extremely rare and breeding this crop is far too difficult for amateur breeders.
Agriculture: Agriculture was independently discovered and developed by many different groups of people in various parts of the world, the main centres being based on the crops wheat (Europe), maize (Central and South America), and rice (Southeast Asia).; Agriculture consists of the propagation and nurturing of domesticated animals and plants. The cultivation of crop plants is now divided into agricultural and horticultural crops. The latter involve a wide array of fruit and vegetables and offer great scope for amateur breeders.; Commercial agriculture is undertaken for financial gain, while subsistence agriculture, mainly in the tropics, is undertaken to feed the farmer’ family, possibly with the sale of some subsistence surpluses. Most subsistence crops also offer great scope for amateur breeders.; Forestry involves the cultivation of trees for timber and it too offers some scope for amateur breeders.
Agrobacterium: Agrobacteriium tumefaciens is the bacterium that causes a disease called crown gall on many different species of host, most particularly on temperate fruit trees. The galls can grow to the size of a soccer ball if left untreated.; Amateur breeders working with rootstocks of fruit trees may care to take resistance to this bacterium into consideration in their breeding. Genetic engineers use this bacterium as a means of introducing foreign DNA into a plant, but this is not a technique for amateurs.
Agro-ecosystem: The ecosystem of a cultivated crop. It differs from the surrounding, natural ecosystem because of the various artificial components of agriculture.
Agro-ecotype: The local landrace of an outbreeding crop is often called an agro-ecotype because, like a wild ecotype, it has responded to selection pressures within its own locality in the agro-ecosystem, and it is well adapted to that locality. In systems terminology, this adaptation is called local optimisation.; In a wide sense, any domesticated variety of plant or animal is an agro-ecotype. Amateur plant breeders may regard their work as improving the domestication of existing agro-ecotypes.
Agronomic suitability: The agronomic suitability of a cultivar is one of the four objectives of plant breeding (the others being yield, quality of crop product, and resistance to pests and diseases).; It is governed by a variety of traits such as plant shape and size (often called crop architecture), time of maturity, suitability for mechanical cultivation and harvesting, frost and/or drought resistance, yield potential, suitability to market requirements, and so on.; This is a factor that amateur breeders must always take into account.
Agronomy: That component of agriculture which is concerned with the theory and practice of growing crops, and with the management of soils.
Aguacate: See: Persea americana.
Air-borne parasites: Plant parasites can be air-borne, soil-borne, water-borne (mainly in irrigation water), and seed-borne. The air-borne parasites include fungi and flying insects, which can sometimes travel for hundreds of miles on prevailing winds.
Akee: See: Blighia sapida.
Aldrin: One of the dirty dozen chemicals called POPS. Aldrin is an insecticide, now banned by international treaty.
Aleurites spp.: Tung, an ancient crop in China, it is now grown in several warm countries. The seeds of A. fordii and A. montana yield a paint oil of exceptional quality. The market has declined from competition with cheaper paints, particularly plastics. Considerable scope for local amateur breeders who are not ambitious about their new cultivars.
Alfalfa: See Medicago sativa.
Alga: (Plural: algae). Primitive plants that have chlorophyll and can photosynthesise. They range in size from single-celled and microscopic, or many-celled and many feet long. They occur mainly in water, which may be either fresh or marine.
Alkaloid: An organic compound containing nitrogen, and with conspicuous physiological properties. Well-known alkaloids include nicotine, caffeine, quinine, morphine, cocaine, and strychnine.
Allele: The alternate copies of a single gene. Each gene normally consists of two alleles. Each allele occurs on one of the two matching chromosomes, one of which comes from the male parent, and the other from the female parent.; In one individual, the two alleles may be both dominant (AA), both recessive (aa), or one of each (Aa). The first two of these combinations are described as homozygous; the third is heterozygous.
Allelopathy: A mechanism that reduces or eliminates competition from other species by the production of toxins. The best known example is that of antibiotics produced by fungi to suppress the growth of bacteria. Equally familiar is the effect of a carpet of pine needles in suppressing the germination of other plants.
Alliaceae: The botanical family that includes the onions and their relatives. However, some taxonomists prefer to classify Allium spp. within either the Liliaceae or the Amaryllidaceae.
Allium ampeloprasum: Leeks and ‘elephant’ garlic. Leeks are tetraploids (4x) and set seed freely, while ‘elephant’ garlic is a hexaploid (6x) and is sterile. We can certainly consider the possibility of breeding leeks for horizontal resistance, but we should steer clear of ‘elephant’ garlic. The breeding procedures are those of open-pollinated crops.
Allium cepa: The common onion, including the shallot. This vegetable is an excellent subject for breeding by amateurs.; There are many different types of onion, ranging from sweet to pungent, and from deep red, and green, to white. And there are many parasite problems of onions, all of which can be either solved or greatly ameliorated by breeding for horizontal resistance.; Onions are open-pollinated but flower only in their second season. The parasite screening should be undertaken in the first season and it should be based on both yield and appearance after exposure to major infestations of parasites.; The best selections are stored, and this constitutes a second screening for resistance to storage rots and pests. The storage survivors are planted out and allowed to flower, but a negative screening decapitates the worst plants, and only the best individuals can form pollen and seed.; New varieties can consist of either improved populations (synthetic varieties) or hybrid varieties. The latter procedure requires more work but has the advantages of higher yields and complete protection of seed production.; The wild progenitors of onion are extinct.
Allium sativum: Garlic. This crop cannot be recommended for amateur breeders as it never sets seed, and it can be propagated vegetatively only. The flowers sometimes produce small bulbils, which can be used for propagation, but these are also vegetative and are not the result of pollination.; The formation of flowers and seeds is a major physiological sink that severely reduces the yield of vegetative parts of the plant. Ancient cultivators probably had a gut-feeling about this, and preferred clones that did not produce flowers or seed.; Garlic provides an excellent example of the durability of horizontal resistance because all the varieties are ancient clones that have been cultivated for centuries without crop protection chemicals, and without serious loss from parasites. Any modern problems with parasites are the result of an environmental erosion of horizontal resistance.
Allium schoenoprasum: Chives. The leaves are used as a garnish. This species is an outbreeder and is easy to breed. Chives can be propagated either vegetatively or from true seed. Chives do not have well-formed bulbs but they do form tillers to produce dense clumps of plant. Easy to breed.
Allogamy: Greek; allo = other, or different; gamy = marriage. The term means cross pollination. An allogamous plant or species is one in which cross-pollination is normal or even obligatory. Cultivated allogamous species include maize, sorghum, millets, and rye; members of the onion family, members of the cucumber family; and various pulses and vegetables.; The converse term, meaning self-pollination, is autogamy.
Allo-infection: Infection is the contact made by one parasite individual with one host individual for the purposes of parasitism. Allo-infection (Greek: allo = other or different) means that the parasite has arrived from somewhere else; it had to travel to its host. The first infection of any host individual must be an allo-infection.; The gene-for-gene relationship provides a system of locking which ensures that most allo-infections are non-matching infections. This is the sole function of vertical resistance in a wild pathosystem.; See also: Auto-infection, Allogamy.
Allopatric: Species, ecotypes, or pathotypes that come from another part of the world.
Allopolyploid: A polyploid has more than two sets of chromosomes (e.g., triploid, tetraploid). In an allopolyploid, the chromosomes are derived from two or more different species. In an autopolyploid, all the chromosomes are derived from the same species.
Allotetraploid: An allotetraploid has four sets of chromosomes derived from two different diploid species. For example, Coffea arabica is believed to be an allotetraploid derived from a cross of the two diploid species Coffea canephora and Coffea eugenioides.; An interspecific cross is usually sterile, but the cross can be made fertile by doubling its chromosome number, and making it an allotetraploid. However specialists should be consulted before such a breeding approach is attempted by amateur breeders in other crops.
Allspice: See: Pimenta dioica.
Alocasia macrorrhiza: One of the aroids, of minor significance, cultivated in S.E. Asia.
Almond: See: Prunus amygdalus.
Alternaria: This genus is an imperfect fungus (i.e., it has no sexual stage) with an extremely wide host range.; Various species of Alternaria cause leaf and fruit spots on citrus, brassicas, flax, potatoes, tomatoes, leeks, onions, and other crops. The spots form concentric rings of colonisation and the disease is often called ‘ring-spot’ or ‘target spot’.; It is easy to accumulate horizontal resistance to this fungus and plant breeders should take it into account when breeding many species of vegetables.
Amaranth: See: Amaranthus.
Amaranthus: Amaranth is an ancient crop of the Americas cultivated either as a grain crop or as a pot herb. It is now a popular ornamental. The Spanish tended to prohibit its cultivation as they believed it was associated with cannibalism, but its full potential is now being recognised.; The grain amaranths consist of three species, A. hypochondriacus and A. cruentas that originated in Mexico and Guatemala, and A. caudatus, which is native to Andean countries such as Peru. Vegetable amaranths are boiled as greens and include A. tricolor, A. dubius, and A. cruentus.; Most amaranths have high levels of horizontal resistance to all their pests and diseases but there is considerable scope for improvements in yield, quality, and agronomic suitability, including possible day-length changes.; The amaranths are wind-pollinated and should be subjected to open-pollinated breeding techniques. An attractive crop for plant breeders.
Amateur plant breeding: Plant breeding that is undertaken by people who are not professional plant breeders, and who may not have any formal training in plant breeding. Using the techniques of horizontal resistance breeding, amateur breeders can easily achieve outstanding results.; The Open Plant Breeding Foundation is here to support this type of breeding -- both with information and practical assistance -- as well as to encourage other plant breeders associations.
Ammonium nitrate: An artificial fertiliser that is exceptionally rich in nitrogen. Ammonium nitrate must be handled with care, as it is powerfully explosive when mixed with a combustible such as oil.
Amphidiploid: An alternative term for allotetraploid.
Amphimictic: The adjectival form of amphimixis.
Amphimixis: The converse of apomixis, and meaning reproduction by seed which has been produced by a normal sexual fusion.
Anacardiaceae: Family of tropical trees that includes mango and cashew.
Anacardium occidentale: Cashew nut. Although it is frost-susceptible, cashew is one of the hardiest of trees and, in warm countries, will grow on poor soils that are unsuitable for other crops. The nuts fetch a high price and the crop is about as valuable as arabica coffee. However, a factory is necessary for the specialised task of shelling the nuts.; Each nut is borne externally on the end of a fairly large fruit. The fruit is edible, but very astringent, and it can be utilised for the manufacture of alcohol. There is a correlation between total yield and quality, the highest yielding trees producing small nuts of low commercial quality.; But there is great variation among trees, and there is scope for selection within existing orchards, by amateur breeders, with a view to vegetative propagation of selected clones.
Anaerobic: Living conditions in which there is an absence of oxygen. Organisms which do not require oxygen are labelled as anaerobic organisms. The converse, meaning with oxygen, is aerobic.
Analogous evolution: Evolution in which similar features have different origins (e.g., the wings of birds, insects, and bats represent analogous evolution). This is the converse of homologous evolution, in which similar features have a common origin (e.g., all the plants in one family have a common ancestor).
Ananas comosus: Pineapple. This is a very difficult crop to breed and it is definitely not recommended for amateur plant breeders.
Anastomsis: Natural grafting that can occur in either stems or roots. For example, mango seeds contain both a nucellar embryo and a normal embryo that is the result of open-pollination. Trees growing from casually discarded seeds often consist of two trunks joined at the base by anastomosis. One trunk is the nucellar seedling and is identical to the maternal parent, while the other is an open-pollinated variant and is visibly different in many characteristics, including fruit quality and resistance to parasites.
Ancient clones: The importance of ancient clones is that they provide proof of the durability of horizontal resistance. Such clones may date from centuries, even millennia, ago.; They are common in figs (Ficus), olives (Olea), date palms (Phoenix), citrus (Citrus), horseradish (Armoracea), garlic (Allium), ginger (Zingiber), turmeric (Curcuma), saffron (Crocus), rhubarb (Rheum), etc.
Andromonoecious: Having both male and hermaphrodite flowers on the same plant.; See: Cucumis melo.
Anethum graveolens: Dill. See also: curry powders.
Angiosperm: Seed-forming plants whose seeds are protected by a seed-coat. This group includes the flowering plants, both monocotyledons and dicotyledons, and it provides virtually all human food, either directly as vegetable matter, or indirectly, as meat.; A few Angiosperms are parasitic on other plants. They lack chlorophyll and they include dodder (Cuscuta spp.), broomrape (Orobanche spp.) and witchweed (Striga spp.). It is possible to breed crops for horizontal resistance to these parasitic Angiosperms. See also: Gymnosperm.
Annual plant: A plant which flowers, fruits, and dies in one season.
Anther: The male reproductive part of a flower that produces pollen.
Anthesis: The time of pollen production.
Anthracnose: A plant disease caused by a species of the fungus called Colletotrichum (pronounced coll-ee-TOT-tree-coom). The symptoms are sunken lesions, several millimetres in diameter, with small, black, sporulating, fungal bodies on the sunken surface.
Antibiotic: A substance that inhibits the growth of micro-organisms, e.g., penicillin. It seems that all antibiotics provide an unstable protection when used singly, and that a cocktail of different antibiotics is much more stable.
Aphids: Plant parasitic insects of the Order Homoptera which are among the most common, and serious, of insect pests of crops.; Also known as greenfly or green bugs, aphids have several different forms, including winged females for allo infection; wingless, asexual, viviparous females for auto-infection; and winged males and females for sexual reproduction.; Many species of aphid are heteroecious. Many are vectors of virus diseases.
Apical dominance: The suppression of lateral branches by the apical shoot, or apex, of the plant.
Apical meristem: The meristem at the main growing point, or apex, of a plant.
Apis: The genus to which honey bees belong. These are stinging, social, hymenopterous insects, useful in the production of honey, and in the pollinating of many species of crop. Amateur breeders can often make use of them to produce a random polycross.
Apium graveolens: Celery and celeriac. An ancient domestication known to the classical Greeks. Celery is used for its green stems, mainly as a flavouring in soups and salads. Celeriac (var. rapaceum) is grown for its swollen, edible roots.
Apomictic: The adjectival form of apomixis.
Apomixis: Greek: apo = without; mixis = mixing. Asexual reproduction by seeds produced from the maternal tissue of a flower.; Apomictic seeds occur mainly in grasses, and they have the advantage of being the equivalent of vegetative propagation, being free of most vegetatively transmitted diseases (particularly viruses).; The so-called ‘apomictic gene’ is a topic of interest among molecular biologists because it could very easily preserve agricultural characteristics, including hybrid vigour, in heterozygous seeds of open-pollinated crops.
Apothecium: An open fruiting body shaped like a ‘dry martini’ glass, produced by some Ascomycetes, with asci on the open, upper surface. Sometimes called ‘cup fungi’.
Apple: See Malus.
Apple scab: See Venturia inaequalis.
Apricot: See Prunus armeniaca.
Araceae: The family to which the aroids belong; see Alocasia, Colocasia, Cyrtosperma, and Xanthosoma
Arachis hypogea: The peanut, also known as ‘monkey nut’, and groundnut, because the plant thrusts its pods underground as a method of self-sowing.; Originating in South America, ancient domestication produced non-fragile pods and shorter pod-bearing stems. Like the non-shattering character in cereals, these changes made harvesting much easier.; Most groundnut varieties are inbreeders and cross pollination is rather difficult. They are also allotetraploids and crossing with wild diploids is not easy. However, many interspecific crosses have been made and these offer considerable scope for development. A serious challenge for amateur breeders but one with great potential for the courageous.
Arachnid: A member of the Arachnida, the class of arthropods that includes spiders, mites, scorpions, and ticks.
Archetype: The wild ancestor of a modern cultivar.
Areca catechu: This palm is the source of the betel nut, which is chewed as a narcotic by more people than use chewing gum. It is chewed as a ‘quid’ of betel pepper leaves with a dash of slaked lime. This ‘quid’ turns the saliva red and this colours walls and sidewalks from spitting.; The young palm is also a popular houseplant. There is some scope for amateur breeders to select superior palms within existing populations in areca-producing countries.
Areca palm: See: Areca catechu above.
Armillaria: Armillaria mellea is known as the honey fungus, and it can cause a serous disease of many species of tree.; It produces long black rhizomorphs that look like boot-laces, and that can grow through the soil and spread the disease from tree to tree. Armillaria often produces toadstools on dead tree stumps.; In the tropics, it occurs only at high altitudes. It has even been postulated that a large network of rhizomorphs constitutes the largest living organism. Foresters often ring-bark trees about a year before felling them, and this denudes the roots of nutrients. The fungus is then unable to invade them.; Another defence is to dig trenches that the rhizomorphs cannot cross. However, many pathologists think that Armillaria will only attack trees that are weakened from some other cause such as waterlogging or shallow soil.; It is not feasible for amateurs to breed for horizontal resistance to this disease.
Armoracia rusticana: Horse radish. The roots are used to make a peppery condiment, but this species does not flower or set seed. It is definitely not recommended for amateur plant breeders.; There are many clones with widely varying degrees of pungency. These ancient clones have few pests or diseases and they are a good example of both the effectiveness and the durability of horizontal resistance.
Aroids: Aroids are a group of tropical root crops belonging to the family Araceae. See: Alocasia, Colocasia, Cyrtiosperma and Xanthosoma.
Arrowroot: See: Maranta arundunacea.
Arrowroot, Queensland: See: Canna edulis.
Arsenic: Compounds of this well-known poison were frequently used as an insecticide before the days of the much less hazardous modern synthetic insecticides.
Arthropod: An invertebrate animal belonging to the Phylum Arthropoda, which includes insects, spiders, crustaceans, centipedes, and millipedes. This is the largest phylum and it contains more than one million known species.; Arthropods are characterised by an exoskeleton with a segmented body and jointed limbs.
Artichoke, globe: See: Cynara scolymus.
Artichoke, Jerusalem: See: Helianthus tuberosus.
Artificial fertilisers: The term ‘fertilisation’ has two meanings in agriculture. It can mean sexual fertilisation of either plants or animals, or it can mean manuring of crops.; Fertilisers used for manure are divided into the two categories of organic and artificial. Organic manures are either the excrement of farm animals, usually known as farmyard manure (F.Y.M.) or stable dung, bone meal, or quarried deposits of fish-eating bird excrement, known as guano.; Artificial fertilisers are produced in factories, usually by a modification of natural products, such as atmospheric nitrogen, rock phosphate, or potash. Their constituents are known as N, P, and K, the symbols standing for nitrogen, phosphorus, and potassium. Other constituents may include calcium and magnesium, as well as various minor nutrients and trace elements.; Artificial fertilisers are not used in organic farming.
Artificial selection: Genetic selection which is controlled by people, within a genetically diverse population. Artificial selection is the basis of both domestication, and modern plant and animal breeding. See also: natural selection, agro-ecotype.
Artocarpus altilis: Breadfruit, which is an ancient domestication and is the staple food in a number of Pacific Islands.
Ascomycete: Fungi whose sexual reproduction is by means of an ascus. Many plant pathogens are Ascomycetes, such as the powdery mildews, and apple scab (Venturia inaequalis).
Ascospore: A spore produced within an ascus. Ascospores are haploid, being the result of the reduction division (meiosis) of a newly fertilised diploid cell, which is the only diploid component in the life cycle of an Ascomycete.; Being the result of meiosis, an ascus usually contains eight ascospores but, in some species, the ascus contains only four, or two ascospores.
Ascus: The microscopic reproductive organ of an Ascomycete fungus. The ascus consists of a tube containing eight, four, or two haploid ascospores that are the result of meiosis. When the ascospores are mature, the tube bursts at its tip, from internal pressure, and the ascospores are projected into the atmosphere like microscopic bullets.
Asexual reproduction: Reproduction without sex. Asexual reproduction prevents variation and it produces clones. Many microscopic organisms, such as viruses, bacteria, and imperfect fungi, have asexual reproduction only.; Many r-strategists plant parasites, such as fungi and aphids have both sexual and asexual reproduction. This has the advantage of speed and economy for the parasite, and it permits a population explosion.; If continued for too long, asexual reproduction in the higher organisms is a survival disadvantage in a wild population, but it can be very useful in agriculture. The asexual propagation of plants by cuttings, grafts, etc., is called vegetative propagation.; Some Angiosperms have asexual reproduction by apomictic or nucellar seeds.; See also: r‑strategists.
Asparagus officinalis: A dioecious vegetable that is perennial cultivated for its young succulent shoots. Difficult to breed and not recommended for amateurs.
Asparagus pea: See: Psophocarpus tetragonobolus.
Asynchronous flowering: The production of flowers at different times within one season. Asynchronous flowering assists cross-pollination. It also assists survival, if there is bad weather that hinders pollination.
Attention deficit hyperactivity disorder (ADHD): The syndrome in children which, as its name implies, exhibits hyperactivity and a very short attention span. It has been reported that about two million children suffer from this syndrome in the United States.; It is thought that the cause of the syndrome may be exposure to hormone mimics during foetal development and/or childhood. There have been numerous documented cases in which a switch to an organic diet has eliminated ADHD and other mental disorders.; See also: Dirty dozen, POPS.
Aubergine: See: Solanum melongena.
Austronesian family of languages: Also known as the Malayo-Polynesian family of languages, these are the languages of remote islands extending from Madagascar, in the West, to Easter Island, in the East, and from Hawaii, in the North, to New Zealand, in the South.; The Austronesian people spread these languages by their ability to make long ocean voyages long before either the Chinese or the Europeans developed ocean-going ships.
Autocratic plant breeding: The converse of the democratic plant breeding produced by self-organising crop improvement. Autocratic plant breeding is justified by the expense of breeding for vertical resistance, and by the relatively few cultivars produced by such breeding.; These cultivars have a very wide ecological adaptation and their widespread use justifies their cost. But the farmer has few choices of cultivar, and the breakdown of a vertical resistance can lead to widespread damage.
Autoecious: The converse of heteroecious, which means that a rust or an aphid is obliged to change its species of host in order to complete its life cycle. An autoecious rust is one that completes its entire life cycle on one species of host.; Entomologists use the term ‘monoecious’ in place of autoecious when describing aphids. Unfortunately, in botany, monoecious means that separate male or female flowers occur on a single plant (See also dioecious, hermaphodite).
Autogamy: (Greek: auto = self; gamy = marriage). Self-fertilisation, or self-pollination. An autogamous species is one in which individual flowers, or plants, are fertilised with their own pollen. However, some cross pollination always occurs in an autogamous species and variability is always maintained. (See also: allogamy).
Auto-infection: Infection is the contact made by one parasite individual with one host individual for the purposes of parasitism. Auto-infection (Greek: auto = self) means that the parasite was born on (or in) the host that it infects; it had no need to travel to its host.; Auto-infection is possible only after a matching allo-infection has occurred. The parasite then reproduces asexually to produce a clone in which all individuals are identical. It follows that, in terms of the gene-for-gene relationship, all auto-infection is matching infection. Consequently, vertical resistance cannot control auto-infection, which can be controlled only by horizontal resistance.; Because all parasitism involves auto-infection, it must be concluded that horizontal resistance occurs in every host, against every parasite of that host.; (See also: allo infection, autogamy).
Autopolyploid: A polyploid has more than two sets of chromosomes (e.g., triploid, tetraploid). In an autopolyploid, all the chromosomes are derived from the same species. In an allopolyploid, the chromosomes are derived from two or more different species.
Auxin: Auxins are plant hormones.
Avena fatua: Wild oats. This species can be a serious weed as it is difficult to control in cereal crops.
Avena sativa: Cultivated oats. This species is a hexaploid and the first controlled crosses were made by a Scottish farmer, Patrick Sheriff, in 1860.; Subsequently, most professional work has used pedigree breeding and back-crossing with a view to introducing vertical resistances. However amateur breeding for horizontal resistance is entirely feasible and a male gametocide, as used with wheat, will probably be effective.
Average: The mean. A figure obtained by dividing the total of given amounts by the number of amounts in the set.
Avocado: See: Persea americana.
Axil: The upper angle between a leaf and the stem.
Axillary bud: A bud that is located in an axil. Many axillary buds are suppressed by auxins emanating from the apical meristem, and they develop only if the apical meristem is damaged or removed.

Glossary: B

Back-crossing: A Mendelian breeding technique designed to transfer a single gene, usually a resistance gene, from a wild plant into a cultivar.; The cultivar and the wild plant are cross pollinated to produce a hybrid progeny. A hybrid individual that carries the resistance gene is then back-crossed with the cultivar parent to produce a second breeding cycle. This process of back-crossing is repeated for several breeding cycles until the hybrid is indistinguishable from the cultivar parent, except that it carries the resistance gene from the wild parent.; Note that back-crossing is an excellent technique when breeding for vertical resistance, but that it dilutes polygenically inherited characters, and it should not be used when breeding for horizontal resistance.; See also: Pedigree breeding.
Bacteriocide: A pesticide that kills bacteria.
Bacteriophage: A virus that attacks bacteria.
Bacterium: A bacterium (pl. bacteria) is the most primitive of the cellular organisms. About 1,600 species of bacteria are known to science and some of these are parasitic on plants.; Bacteria are prokaryotes. That is, although their cells do contain DNA, they do not contain a nucleus.
Bajra: See: Pennisetum typhoides.
Balanced science: Balanced science means two things. First, all systems levels are treated equally. Second, factual science and theoretical science are treated equally.; One of the reasons that twentieth century crop science has become unbalanced is because both the higher systems levels and theoretical aspects have been neglected. See also: Suboptimisation.
Bambara groundnut: See: Voandzeia subterranean.
Bamboo: See: Gramineae.
Banana: See: Musa.
Barley: See: Hordeum vulgare.
Barberry: See: Berberis.
Basidiomycete: A group of fungi whose microscopic spores, called basidiospores, are produced externally on microscopic structures called basidia. The basidium is the result of sexual recombination, and it usually produces four haploid spores by reduction division.; This group includes all toadstools and mushrooms as well as a number of plant pathogens.
Basidiospore: A microscopic spore produced at the end of a basidium by a Basidiomycete. These spores are usually produced in groups of four, and they are the result of sexual recombination followed by reduction division.
Basidium: A microscopic, club-shaped structure on which basidiospores are produced.
Bast fibre: Any coarse plant fibre used for making ropes, sacking, or mats (e.g., hemp, jute, sisal).
Batatas: See: Ipomea batatas.
Beans: See: Glycine (soybean), Phaseolus (haricot and other beans), Vicia (broad bean, or faba bean).
Bed bugs: A wingless hemipterous bug, belonging to the genus Cimex, which sucks human blood, and infests beds and dirty houses.; It is of interest because centuries of use of dried flowers of Chrysanthemum cineriifolium in Dalmatia have proved that natural pyrethrins are a stable insecticide.
Beech: See: Fagus sylvatica.
Beehives: Amateur breeders wishing to obtain a massive random polycross in an outbreeding species that is pollinated by bees, will usually benefit from placing a beehive close to their field plots.; If you do not wish to handle bees yourself, a friendly beekeeping neighbour can probably be found to assist.; Bees will also achieve a significant amount of cross-pollination in an autogamous species such as beans, but the use of a marker gene is recommended.
Bees: See: Apis.
Beet: See: Beta vulgaris
Beet, sugar: See: Beta vulgaris.
Beetles: Insects of the Order Coleoptera characterised by hard fore-wings which meet in a straight line down the back, and cover the hind wings. Many beetles are serious crop parasites, and others are serious parasites of stored food products.; Some beetles, such as ladybirds, are beneficial in that they eat other crop parasites.; There are some 300,000 species of beetles in the world, and this is by far the largest order of living organisms.
Bell-shaped curve: The graph that is produced when various levels of a quantitative character that has a normal distribution (e.g., horizontal resistance) are plotted against their frequency.
Benincasa hispida: The white, or wax, gourd, which is a member of the Cucurbitaceae.
Berberis spp.: The wild barberry that is the alternate host of the heteroecious wheat stem rust (Puccinia graminis). Barberry is the winter host in which sexual recombination occurs, and new vertical pathotypes are produced. See also: Saturation technique.
Bergamot oil: This essential oil is extracted from the rind of the Bergamot variety of Citrus aurantium, and is used to scent Earl Grey tea. The name derives from the town of Bergano in northern Italy. An inferior bergamot oil is obtained from the labiate herb Mentha citrata.
Berry: A fruit containing no hard parts except the seed, e.g., tomato, banana, grape, date, gooseberry.
Berry fruits: See: Rubus spp.
Bertholletia excelsa: Brazil nut. A young seedling of this tree takes at least twenty years to bear its first fruit, and may take as long as eighty years. The fruits take a year to ripen. Definitely not a crop for amateur plant breeders.
Beta vulgaris: This species, which belongs to the family Chenopodiacea, has been domesticated into sugar beet, garden beets (beetroots), fodder beet, mangolds, and chards. It is open-pollinated and breeding is based on recurrent mass selection.; The German chemist Marggraf first observed sugar in fodder beets and his pupil Achard started improving the crop and developing extraction techniques. Napoleon encouraged beet sugar production during the British naval blockade, which prevented the import of cane sugar from the West Indies. Subsequent tariff protection of various European and North American beet sugar industries did much to stimulate production. Beet sugar now makes up about half of the world supply of crystalline sugar.; The accumulation of resistance to ‘curly top’ virus in North America was a good example of very rare twentieth century breeding for horizontal resistance. Recent breeding has produced ‘monogerm’ varieties which have only one seed in each fruit. These are important as they eliminate the need for hand-thinning, and they allow the total mechanisation of the crop. However, this degree of technicality has taken the crop out of the hands of amateur breeders.; Beetroots, fodder beet, mangolds, and chards offer scope to the amateur breeder working with horizontal resistance.
Betula spp.: Birch trees, used in plantation forests to produce hardwood. Not recommended for amateur breeders.
Biennial: A plant which requires two seasons to flower, fruit, and die.
Biffin, R.H.: The scientist in Cambridge who first discovered single-gene resistance and initiated a century of professional plant breeding for vertical resistance.
Billion: The term billion should be used in the more logical American sense to mean one thousand million (10⁹), rather than the somewhat idiosyncratic British sense of one million million (10¹²) which is called one trillion in North America.
Bimli jute: See: Hibiscus cannabis.
Bimodal rainfall: A tropical pattern of seasons in which there are two rainy seasons, and two dry seasons each year.
Binomial coefficients: The numbers that make up the lines in Pascal’s triangle. The largest binomial coefficient for a given number of pairs of genes in the gene-for-gene relationship, is the number of biochemical locks and keys obtained in the n/2 model.
Bioassay: The testing or measuring of a substance with living organisms. For example, the toxicity of an insecticide can be determined by measuring its effects on living insects.
Biochemical key: A term sometimes used to describe the vertical parasitism genes in an individual parasite. Its biochemical key either does or does not fit the biochemical lock of the host that it is allo infecting.; This is the operation of the system of locking of the gene-for-gene relationship in a wild plant pathosystem, according to the n/2 model. Its function is to reduce the frequency of allo-infections that are matching infections, thus reducing the population explosion of an r-strategist parasite.
Biochemical lock: A term sometimes used to describe the vertical resistance genes in an individual host. Its biochemical lock either does or does not match the biochemical key of the parasite that is allo infecting it.; This is the operation of the system of locking of the gene-for-gene relationship in a wild plant pathosystem, according to the n/2 model. Its function is to reduce the frequency of allo-infections that are matching infections, thus reducing the population explosion of an r-strategist parasite.
Biochemistry: The chemistry of living processes.
Biodiversity: Any aspect of biological diversity, including ecosystems, and their diversity of species, ecotypes, etc. The term is relevant to the ecological principle that diversity provides stability.
Biological anarchy: The loss of biological control that occurs when pesticides kill the hyper-parasites, predators, competitors, antagonistic organisms, or other biological control agents of a crop parasite.; Biological anarchy is probably a phenomenon of much greater importance than has been realised in the past. When the effects of biological anarchy are considerable, a restoration of biological controls causes a major reduction in parasite damage, and this is the basis of integrated pest management (IPM).; Because the use horizontal resistance restores biological controls, the phenomenon of biological anarchy suggests that we may need considerably less horizontal resistance than we may think in order to obtain a complete control of various crop parasites.
Biological control: The control of crop parasites that is exerted by predators, hyper-parasites, competitors, antagonistic organisms, and other agents.; The effects of this control can be diminished or lost entirely by the use of crop pesticides. This loss of biological control that occurs with pesticide use is called biological anarchy.; The proponents of integrated pest management (IPM) rely on restoring lost biological controls. These losses may be more important than many people realise. They also suggest that we may need rather less horizontal resistance than we may think in order to obtain a complete control of crop parasites, because the biological controls will be restored once pesticide use stops.; The best means of restoring biological control is by the use of horizontal resistance; and the best means of enhancing horizontal resistance is by restoring biological control. The two effects are mutually reinforcing.
Biological order: A term from modern complexity theory. It means that the self-organisation is fully functional and operating.; The n/2 model is the result of self-organisation and, when functioning, is an example of biological order.; Parasitism is not competition between host and parasite, nor is it cooperation; it is biological order.
Biology: The study of living organisms.
Biomagnification: The phenomenon in which a toxin, such as DDT, accumulates as it moves up the food chain. This happens because an individual eats small amounts of the toxin with each meal but does not excrete it. The levels of toxin thus increase from minute traces in, say, lake water, to very high levels in fish-eating birds that are at the top of the food chain. It is a sobering thought that humans are at the top of their own food chain.
Biomass: The total weight of one or more named organisms within a particular area.
Biometrician: (Greek: bio = life; metrics = measurements). A member of the biometrical school of genetics, in contrast to the Mendelian school.; Biometricians study the inheritance of quantitatively variable characters controlled by polygenes. This school developed population breeding methods using recurrent mass selection, and it employs horizontal resistance.; In more general terms, biometry is any quantitative analysis of biological phenomena.
Biosphere: A term coined by the Viennese geologist Eduard Seuss (1831-1914) in 1875 to describe that part of the Earth’s surface where life occurs.; The term was used in 1926 by Vladimir Vernadsky (1863-1945) as the title of his book on this subject. This work was an early example of the holistic approach but, because of political problems and the Cold War, it remained largely unknown in the West until recently.; See also: Gaia hypothesis.
Biotechnology: The use of micro-organisms, which are often genetically engineered, for industrial and pharmaceutical purposes.
Biotrophic: A biotrophic parasite is one that obtains nutrients from the living tissues of its host, as opposed to a necrotrophic parasite, which kills those tissues with toxins before consuming them.
Biotype: A subdivision of a species in which all individuals are morphologically identical but physiologically (or parasitologically) dissimilar. Entomologists tend to refer to vertical pathotypes of insects as ‘biotypes’, but the term is imprecise.
Birch: See: Betula spp.
Birth rate: The rate at which a population is gaining individuals. This rate is an important factor in the development of epidemics and infestations in crops. See also: death rate, population growth.
Bisexual: In botany, this term means that both sexes are present and functional in one flower.
Bixa orellana: Annatto, a tropical American shrub which is cultivated as a food colouring.
Blackberry: See: Rubus spp.
Black currant: See: Ribes.
Black gram: See: Phaseolus mungo.
Black pepper: See: Piper nigrum.
Blast: Possibly the most important disease of rice, caused by the fungus Pyricularia oryzae.
Blastofaga psenes: The fig wasp. See: Ficus carica.
Blemishes: Blemishes on fruit and vegetables are often caused by crop parasites. Since the development of synthetic crop protection chemicals, it has become fashionable to see only blemish-free produce on sale. However, blemishes are an indication of freedom from pesticides and are more accepted for this reason by lovers of organic food.
Blighia sapida: Akee, a West African tree with poisonous fruits. However, the white arils from naturally matured fruits are edible. Now common in the West Indies.
Blight: The common name of many plant diseases, usually caused by the downy mildews (Peronopsorales). The symptoms of most blight diseases are a burning and necrosis of the leaves.; Potato blight (Phytophthora infestans), which caused the Irish famine during the ‘hungry forties’ of the nineteenth century, is the most famous of the blight diseases and, possibly, the most famous plant disease of all.
Blood: See: Dried blood.
Blueberry: See: Vaccinium spp.
Boehmeria nivea: Ramie, a perennial grass with strong stem fibres extracted as a bast fibre.
Boll worms: There are several different insects that attack cotton bolls, and are known as boll worms.
Bonavist bean: See: Dolichos lablab.
Bone meal: An organic phosphate fertiliser produced by roasting animal bones that are usually obtained from an abbatoir.
Boom and bust cycle: A term applied to the cycle of success and failure in the use of vertical resistance in professional plant breeding.; The term has also been applied to the manufacture of unstable pesticides that fail on the appearance of a resistant strain of the pest.
Bootlace fungus: Common name for Armillaria mellea.
Bordeaux mixture: The first, and also the most spectacularly successful, of all man-made fungicides, discovered in Bordeaux, France, by Millardet, in 1882.; The mixture is prepared by mixing a solution of copper sulphate with freshly slaked lime. This fungicide saved the French wine industry from ruin by the newly introduced downy mildew (Peronospora viticola), and it also controlled potato blight, caused by Phytophthora infestans.
Borlaug, Norman: Breeder of the miracle wheats and winner of the 1970 Nobel Peace Prize.
Boron: Boron is an important plant nutrient although its physiological function is poorly understood. Boron deficiency causes many growth distortions. If boron deficiency is suspected, a specialist should be consulted.
Botanical insecticides: There are five natural insecticides derived from plants. These are nicotine, pyrethrins, rotenone, ryania, and sabadilla.
Botrytis: A microscopic fungus which is a facultative parasite on many species of crops, particularly on fruit and vegetables, and especially during very humid weather.; It usually causes a disease called grey mould, and it is mostly a necrotrophic pathogen (i.e., it kills host tissue with toxins before invading and obtaining nutrients from them).; The fungus often produces sclerotia from which apothecia bearing asci sometimes develop. It is consequently considered an Ascomycete, even though asci have never been observed in some species.
Bougainville: Antoine de Bougainville (1729-1811) was the first Frenchman to circumnavigate the world. The island of Bougainville, largest of the Solomon Islands in the South Pacific, is named after him. So is the ornamental plant Bougainvillea.
Bougainvillea: A tropical genus native to South America and much used throughout the tropics and subtropics as an ornamental.; The plant is a woody, climbing shrub with many prominent ‘flowers’ that are really bracts concealing the very small true flowers. These bracts vary in colour from bright red, through orange and yellow, to white.; Not difficult to breed and a fun project for amateur breeders in suitable climates.
Bouillie bordelaise: See: Bordeaux mixture.
Brassica alba: (Syn. Sinapis alba) White mustard. This is a ‘hot’ mustard, as opposed to the three species (B .juncea, B .nigra, & B .carinata) which are ‘pungent’ mustards.; An open-pollinated species requiring recurrent mass selection for breeding.
Brassica campestris: Turnip and Canola. A complex, outbreeding species suitable for amateur breeders working with horizontal resistance.
Brassica carinata: Ethiopian mustard. This crop is confined to the highlands of northeast Africa where it is grown for oil, which is locally known as Noug oil. There is probably scope for amateur breeders to select within existing landraces.
Brassica juncea: Brown mustard, also known as Indian mustard. This crop originated in India and it has secondary centres of origin in China and southern Russia.; This species has the advantage that it can be combine-harvested and, for this reason, has become a major crop in Canada and parts of the northern U.S.A. This area now produces the bulk of the world’s mustard.; B. juncea is self-pollinating and is cultivated as pure lines. While much amateur breeding has occurred in India in the past, mainly for the production of oil, there is little scope for amateur breeders in the cultivars of commercial mustard cultivation.
Brassica napus: Swedes, rutabuga, and rape seed. This species is an allotetraploid derived from a cross of the diploid B.campestris and B.oleracea.; Swedes, which are visually similar to turnips, are a relatively recent crop first recorded in Sweden in 1620.; Rape seed is a somewhat older, European domestication. (Note that the rape seed, known as Canola, is a cultivar of B .campestris).; Suitable for breeding by amateur breeders with special interests, given some assistance from experts.
Brassica nigra: Black mustard. This was the traditional, hand-harvested, European mustard until the mid-twentieth century, when it was largely replaced by B .juncea, which is suitable for mechanical harvesting.
Brassica oleracea: Cabbages, Brussels sprouts, kohl rabi, cauliflower, broccoli, and kales. This is an ancient domestication, and many of these crops were known to the ancient Romans.; It is a complex species probably derived from three wild species with a presumed doubling of chromosome number, followed by the loss of some chromosomes. The species is open-pollinated and requires recurrent mass selection, although some self-pollination occurs with sprouts, cauliflowers, and kohl rabi.; Most of the crops are biennials and breeding by amateurs is feasible although some specialist help will probably be needed. Calabrese, a sprouting broccoli, is B. olearacea var. italica, and it has recently become popular in North America.
Brassica oleracea var. gemmifera: Brussels sprouts. See under: Brassica oleracea.
Brassicas: Members of the Brassica genus of the Crucifereae family, includes broccoli, cabbages, canola, cauliflower, kale, kohl rabi, rape seed, sprouts, turnip, and various mustards. The taxonomy of the various species is confused, and the names given here may not coincide with other accounts.
Brazil nut: See: Bertholletia excelsa.
Breadfruit: See: Artocarpus altilis.
Bread wheat: See: Triticum aestivum.
Breakdown of vertical resistance: A total, qualitative failure of vertical resistance resulting from a matching allo-infection. Being matched, the vertical resistance stops functioning, and it is said to have broken down.; In a wild pathosystem, which has genetic diversity, breakdowns occur only in individual host plants. In a crop pathosystem, which has genetic uniformity, the breakdown involves the entire cultivar, because every allo-infection, from plant to plant within that crop, is a matching infection.; Because some matching always occurs, vertical resistance is temporary resistance. Because horizontal resistance operates against matching pathotypes of the parasite, it does not break down in this way; it is durable resistance.; See also: discontinuous pathosystem.
Breeders association: An association of amateur plant breeders, like the Open Plant Breeding Foundation, who aim to produce crops that can be grown organically without the use of pesticides.; Because it is durable resistance, and is the easiest resistance to work with, we breed for horizontal resistance, using recurrent mass selection in order to increase the levels of resistance to control all local parasites of the crop.; On-site selection is important if the new cultivars are to be in balance with the local agro-ecosystem.
Breeders associations, royalties: In most countries, a breeders association that has produced and registered a new cultivar is entitled to royalties on the sale of propagated material of that cultivar.; The association should establish in advance how royalties are to be used, either to support the association's activities, to be shared among members, or to be used for charitable purposes such as supporting new clubs. Some clubs may choose to put a cultivar in the public domain, but it should still be registered to prevent anyone else from exploiting it.
Breeders associations; neighbour’s complaints: One of the oldest of agricultural disputes is caused by the farmer who allows weed seeds to blow on to their neighbour’s land. The pollen blowing across farm boundaries from open-pollinated plants, that have been genetically engineered, has also become a matter of dispute.; Similar disputes can arise from breeders associations that deliberately encourage pests and diseases, which can then spread on to their neighbours' crops.; The best way to avoid this kind of dispute is to visit your neighbours and explain exactly what you are doing, and why. The basic explanations are as follows:; (i) Soil-borne parasites will not normally spread to the neighbours’ land.; (ii) Water-borne parasites may spread in surface drainage water, or in a stream or river that is supplying irrigation water, but this is a relatively rare occurrence, and can usually be controlled or avoided.; (iii) Minor wind-borne parasites do not matter.; (iv) Major wind-borne parasites are around anyway, regardless of anything the breeder might do and, if the farmer is using pesticide controls, these should not matter. If the neighbour’s spray schedule is not working this is either because of inappropriate techniques, or because a new pesticide-resistant strain of the parasite had appeared. In neither event can the breeder be blamed.; (v) If the farmer is using a cultivar with a vertical resistance that breaks down during the breeding activities, it should be explained that the designated pathotypes used by the breeder are all common races that have been around for some time. The breeder cannot be blamed for a normal failure of vertical resistance on someone else’s land.
Breeders associations; publication: Publication, including on the Internet, serves two possible purposes. One is to exchange either breeding material, or information on techniques. The other is to advertise and distribute a new cultivar.
Breeders’ rights: The plant breeders’ equivalent of authors’ copyrights. These rights earn royalties on the sale of seed of registered cultivars. The breeders’ rights legislation in most countries has a further clause that entitles a breeder to use a registered cultivar in their breeding program. However the regulations under the plant patent legislation of the USA is considerably different in this respect.
Breeding cycle: The complete cycle of events that constitutes one generation of plant breeding. A breeding cycle usually begins with the cross pollination of selected parents, and ends just before the next cross-pollination is due.; There may be several intervening generations which may include a multiplication generation, single seed descent for several generations, and, perhaps, late selection to produce the new parents of the next breeding cycle in an autogamous species.
Brinjal: See: Solanum melongena.
Broad bean: See: Vicia faba.
Broccoli: See: Brassica oleracea.
Bromeliaceae: The botanical family of monocotyledons that includes pineapple.
Bromus inermis: A cultivated fodder grass called ‘Smooth Brome’.
Broom corn: See: Sorghum bicolor.
Broomrape: See: Orobanche spp.
Brussels sprouts: See: Brassica oleracea.
Buckwheat: See: Fagopyrum spp.
Bud: A young shoot, usually protected by scales or bracts, often for over-wintering purposes. Vegetative buds can be used for bud-grafting and meristem culture, but flower buds cannot.
Bud graft: The type of graft in which a vegetative bud is removed from its parent plant and used as a scion to be grafted onto a stock. The bud is normally removed with a portion of green bark, which is then inserted under the green bark of the stock.; This technique is widely used with fruit trees, such as stone and pome fruits, and citrus, as well as other trees such as rubber, in order to grow a susceptible scion on a resistant rootstock. Inter-specific and inter-generic grafts are often possible.
Budding: The process of making a bud-graft. The term can also be applied to the vegetative reproduction of micro-organisms (e.g., yeasts) which multiply by budding.
Bug: In a colloquial sense, a bug is any small organism that is a nuisance. In an entomological sense, however, a bug is an insect that is a member of the Order Hemiptera, characterised by sucking mouth parts. Many bugs are serious crop parasites.
Bulb: An underground storage organ of a monocotyledon in which a shortened stem bears fleshy leaf bases that enclose the next season’s bud. Not to be confused with a corm.
Bulk screening: A technique for obtaining a fair degree of homozygosity for the purposes of late selection. A heterozygous population of an inbreeding species is multiplied for several generations in the field with minimal or zero selection in the early stages.; Such early selection as does occur involves only single gene characters such as marker genes. However, single seed descent in a greenhouse is usually preferable, because it is faster.
Bullo: See: Elusine corocana.
Bullrush millet: Also known as pearl millet, spiked millet, cat-tail millet and bajra. See: Pennisetum typhoides.
Butterfly: Adult insects of the Order Lepidoptera, which have large membranous wings. The wings are covered in scales, which usually confer bright colours on the upper surface of the wings, and these serve as sex attractants. The scales on the lower surface of the wings usually confer camouflage colours.; At rest, the upper surfaces of the wings are displayed to attract a mate. Alternatively, they are pressed together in a plane vertical to the body for purposes of concealment. The fore-wings are normally larger than the hind wings. The long, slender antennae invariably have a clubbed end.; The juvenile stages are known as caterpillars or grubs, and many are serious parasites of crops. The sucking mouthpart (proboscis) of the adult is usually a coiled tube, used for extracting nectar from flowers.; See also: moths.

Glossary: Ca-Cn

C₃, C₄ photosynthesis: There are two different chemical pathways in photosynthesis, known as C₃ and C₄. The former is common while the latter, which occurs mainly in a few tropical plants is rather rare. However, C₄ photosynthesis is much more efficient and is responsible for the high yields of crops such as sugarcane, cassava, and maize.
Cabbage: See: Brassica oleracea.
Cabernet Sauvignon: The principal grape cultivar of Bordeaux, France, producing the red wine known as claret in England. See Vitis vinifera.
CABI: Commonwealth Agricultural Bureaux International. For a fee, the following institutes, which are part of CABI, will identify crop diseases, insects, and nematodes, respectively:; (1) International Mycological Institute, Bakeham Lane, Egham, Surrey, TW20 9TY, England;; (2) International Institute of Entomology, 56 Queen’s Gate, London, SW& 5JR, England;; (3) International Institute of Parasitology, 395A, Hatfield Road, St. Albans, Herts, AL4 0XU, England.
Cacao: See: Theobroma cacao.
Cadang-cadang of coconuts: A lethal disease of coconuts in the Philippines, caused by a viroid. This disease should be considered a grave phytosanitary risk in all other coconut areas.
Cajanus cajan: This tropical pulse, a member of the family Leguminoseae, is called the pigeon pea, also known as red gram, Congo pea, and no-eye pea, and it is a native of Africa.; This crop is self-pollinating with about 20% of out-crossing, usually by bees and other insects.; For controlled hybridisation, the flowers must be emasculated before 9am on the day before the flower opens. They may be hand-pollinated at the time of emasculation.; Pigeon peas have a wide ecological adaptability but they do poorly in the wet tropics and they cannot tolerate frost. Most cultivars are short-day plants. This is a suitable crop for amateur breeders who should usually begin by selecting within local landraces.
Calabash: See: Crescentia cujete.
Calabrese: See: Brassica oleracea var. italica.
Calcium: Calcium is an essential nutrient of plants, and it ranks in importance after nitrogen, phosphate, and potash. Using lime (calcium carbonate) as a fertiliser both adds calcium and lowers the acidity (see pH) of the soil.
Calyx: The outermost covering of a flower, made up of sepals, which may be either united or separate.
Cambium: A layer of active cells that separates the xylem and the phloem. These cells produce the new xylem and phloem that are represented by the annual rings of trees.
Camellia spp.: See: Thea spp.
Camote: See: Ipomea batatas.
Canker: A necrotic, sunken lesion on a thick part of a plant, such as a stem. Cankers are usually caused by fungi.
Canna edulis: Known as ‘achira’ in South America, where it originated, this crop is usually called Queensland arrowroot, or purple arrowroot, in English. It is grown commercially in Australia for extraction of starch from the rhizomes.; Hybrids of wild species of Canna are a popular ornamental known as the Canna Lily. Rather too specialised for amateur breeders.
Cannabis sativa: 1. Hemp. Tall varieties grown especially for the stem fibres. The stems are retted either wet or dry in order to extract the bast fibres, which make up about 25% of the stem tissues. The cultivation of hemp has often been legally restricted because of its close similarity to the drug varieties that produce marijuana (see below). However, the crop is becoming popular and offers scope for amateur breeders in areas where it has not been previously cultivated.; The fibres, gathered from wild plants, have been used since Neolithic times, and the plant has probably been cultivated in China and Central Asia, for fibre production, for more than six thousand years. It is still cultivated in many countries for its fibres, although competition from synthetic fibres has greatly reduced its importance.; 2. Marijuana. Short varieties grown for drug purposes. Known as ‘ganja’ in India, ‘marijuana’ in the Americas, and ‘bhang’ elsewhere, this is a relatively harmless drug plant.; This crop, which is illegal in many countries, provides an excellent example of what can be achieved by amateur breeders. A great number of breeders working independently have increased the strength of the plant’s psychoactive component, tetrahydrocannabinol (THC) by about 100 times the naturally-occurring concentration. But the general advice to plant breeders is to stay legal.
Canola: See: Brassica campestris.
Cantaloup: See: Cucumis melo.
Capsicum spp.: When Columbus reached the Americas, he believed he had arrived in India, and he caused more confusion in European languages than any other person by introducing terms such as ‘Indians’, ‘West Indies’, ‘India rubber’, ‘Indian corn’ (maize), and ‘red pepper’. He was looking for black pepper (Piper nigrum) but all he found were chilli peppers, otherwise known as red, green, sweet, and hot peppers, cayenne, Tabasco, and paprika, which are all members of the genus Capsicum. Chilli peppers are now so popular in countries such as India and China that the people of these countries believe them to be indigenous.; The taxonomy of this genus is very confused and, as most types interbreed freely, the one species Capsicum annuum covers all but a few perennial types known as Capsicum frutescens.; The whole of C. annuum should be regarded as a single hybrid swarm showing immense variation. The plants are mostly self-pollinated with about 15-20% of cross pollination. Pure lines are thus possible and both emasculation and crossing are easy.; Combined with the very wide variation, this ease of working makes it an excellent crop for amateur breeders working in warm climates. There are some quite serious virus and anthracnose disease, as well as several insect pests, that merit breeding for horizontal resistance.; Chillies are another example of a crop with extinct wild progenitors.
Capsid: Leaf or plant bugs of the family Miridae, of the order Hemiptera. Some species are serious pests of cultivated plants.
Carbohydrate: Organic chemicals made up of carbon, hydrogen, and oxygen, such as starch and sugars. Most carbohydrates are produced by plants as a result of photosynthesis, a process that uses chlorophyll and solar energy to combine water and carbon dioxide into carbohydrates, often in the proportion of one carbon atom to two hydrogen atoms and one oxygen atom. Carbohydrates are a major source of dietary energy.
Cardamom: See: Elettaria cardomomum.
Carica papaya: Papaw (often misspelled ‘pawpaw’). The plants are tropical, soft-wooded trees with a relatively short lifespan, cultivated for their fruit and for the extraction of papain, which is an enzyme able to break down protein, and it is used as a meat tenderiser, and as a medical aid to digestion.; The best eating fruit is produced in a very hot climate.; The plants are dioecious but hermaphrodite lines exist. Being open-pollinated, recurrent mass selection is easy, and this is an excellent crop for amateur breeders.; There should be a rigorous negative screening of male trees before anthesis. The only problem is that the plants are rather big, and considerable space is required if a large population is to be screened in each breeding cycle.; There are a number of virus diseases, and breeding for horizontal resistance should be both rapid and easy. Selection within commercial crops might be the most convenient technique, selecting plants with minor symptoms rather than those with no symptoms, as these might be escapes from infection. If feasible, inoculation of all plants in the screening population is advised.; This is one of the crops that has never been found wild, possibly because hunter-gatherers exploited it to extinction while early farmers ensured the survival of domesticated forms. The crop is believed to have originated in Central America, in the area Mexico-Costa Rica.; See also: Extinct wild progenitors.
Carya pecan: Pecans, a native of Mexico and the southern USA. Nuts are still harvested from wild trees but the majority are cultivated as clones. Some scope for amateur breeders selecting among wild trees. The pecan is also the source of hickory wood, in demand for smoking various foods.
Carnivore: An eater of animal tissues; meat-eater. See also: herbivore, omnivore.
Carpocapsa pomonella: The codling moth which attacks apples, producing a grub in the core of the fruit.
Carrot: See: Daucus carota.
Carrying capacity of the environment: There is an absolute limit to the carrying capacity of any natural environment for any wild species. However, the carrying capacity of an artificial agro-ecosystem can be increased considerably above the natural limit by the use of artificially selected (domesticated) species, and artificial cultivation practices, such as weeding, and the use of artificial fertilisers and irrigation.
Carthamus tinctoris: Safflower. A member of the Compositae family, this is a minor oil seed crop, with potential as an ornamental, grown chiefly in India, USA, and Mexico. Suitable for amateur breeders.
Cash crops: A subsistence farmer usually has two categories of crop. Subsistence crops are for the feeding of the farm family; they may also include fodder crops for the farm animals. Cash crops are grown for sale.; As a general rule, a subsistence farmer is poor, and is unwilling to spend cash on subsistence crops, because that cash gets eaten. But cash spent on cash crops is likely to be returned with a profit. One of the many advantages of increasing the yield of subsistence crops is that farmers will have more land available for cash crops.
Cashews: See: Anacardium occidentale.
Cassava: See: Manihot esculenta.
Castanea spp.: Chestnut. The sweet chestnut (C. sativa) is cultivated as selected clones. The American chestnut (C. dentata) has been largely destroyed by the introduced chestnut blight (Endothia parasitica). Various species are prized for their timber. Not recommended for amateur breeders.
Castor: See: Ricinus communis.
Catalyst: A substance that increases the rate of a chemical reaction without being changed itself.
Caterpillar: The juvenile instars of a butterfly or moth.
Cauliflower: See: Brassica oleracea.
Cayenne pepper: See: Capsicum spp.
Ceiba pentandra: Kapoc. A tropical tree that produces seed fibres with a superficial resemblance to cotton. The cotton-like hairs are water-resistant and very buoyant, and they are used mainly as filling for life-jackets. Kapoc is also used for sound and heat insulation.; Unfortunately, the hairs cannot be spun to produce yarn and cloth; if they could, this tree would be a crop of major importance as it far out-yields cotton.
Celeriac: See: Apium graveolens.
Celery: See: Apium graveolens.
Cell: The fundamental unit of plant and animal bodies. Unlike animal cells, plant cells are protected by a cellulose wall. But all cells consist of a membrane enclosing cytoplasm and nuclear material.
Cell wall: In plants, most of the microscopic cells are encased in a protective covering called the cell wall. This covering is usually made of cellulose. See also: Lignin.
Cellulose: The organic chemical that constitutes cell walls. Cotton, for example, is pure cellulose. When it is dissolved in a suitable solvent, such as amyl acetate, which is then evaporated off, cellulose is converted into celluloid, which was a widely used film for photography, and for wrapping food and cigarettes, before the days of synthetic plastics.
Cenchrus ciliare: A subtropical fodder grass native to South Africa.
Centre of diversification: The geographic area in which a crop species shows the greatest diversification. The centre of diversification is often different from the centre of origin, particularly with tetraploids.
Centre of origin: The geographic area in which a crop species was domesticated from its wild progenitors.
Cereals: Cereals are grasses (members of the botanical family Gramineae) that are cultivated for their edible seeds.; The most important cereals are wheat, rice, and maize. Other cereals include millets, sorghum, teff, rye, oats, and barley. See also: pseudo-cereals.
Certified seed: Seed can be certified in a number of ways. True seeds can be certified with respect to their identity, purity, trueness to type, freedom from diseases, and germination percentage. Plant parts used for vegetative propagation (e.g., tubers, setts, rooted cuttings) are often certified in the same way.; Note that a cultivar that requires seed that is certified free from disease is usually very susceptible, otherwise such certification, which is expensive, would not be necessary. One of the many objectives of amateur plant breeding is to develop horizontal resistance to the point that certification for freedom from disease is no longer required.
CGIAR: See: Consultative Group on International Agricultural Research.
Chance escape: For a variety of reasons, some individuals in a screening population may remain free of pests or diseases. Also known as disease escape, this phenomenon can be very misleading because it is so easily confused with resistance.; See also: inoculation, patchy distribution.
Chard: See: Beta vulgaris.
Château Beaucaillon: It was at the Château Beaucaillon, in the Bordeaux district of France, that Millardet, in 1882, discovered Bordeaux mixture, the highly effective fungicide for downy mildews and potato blight.
Chenopodium quinoa: Quinoa, the most important of the grain amaranths, is an extremely variable crop that was domesticated in Central America long before the Spanish conquest.; The three main aspects of its domestication are seeds that are twice as large as the wild progenitors, the elimination of seed dormancy, and the retention of the seeds in the head.; This pseudo-cereal is an interesting example of parallel domestication that is closely similar to that of the Old World true cereals. This is a minor crop but one which offers great scope for amateur breeders.
Cherry: See: Prunus avium.
Chestnut: See: Castanea spp.
Chestnut blight: See: Endothia parasitica.
Chickory: See: Cichorium spp.
Chickpeas: See: Cicer arietinum.
Chiclé: See: Manilkara zapota.
Chicory: See: Cichorium spp.
Chillies: See: Capsicum spp.
Chives: See: Allium schoenoprasum.
Chloris gayana: Rhodes grass; this is the dominant, wild grass in extensive savannas in East and Southern Africa. Selection has produced a number of pasture cultivars both perennial and annual. Some cultivars are turf grasses and make attractive lawns.; This species can be grown over a wide range of habitats and it has been introduced to many areas. It has reasonably high yields of hay, fodder, and grazing. It is palatable to stock. A suitable species for amateur breeders in ecologically appropriate areas.
Chlorophyll: The pigment that makes plants green, and which is the catalyst for converting carbon dioxide and water into carbohydrates, using solar energy, in the process known as photosynthesis. The term is derived from the Greek words for ‘green’ and ‘leaf’.
Chlorotic: A loss or reduction in the green colour of leaves, due either to the destruction of chlorophyll, or to the prevention of its synthesis, usually by the action of a parasite, particularly a virus, or by a mineral deficiency.
Cholam: See: Sorghum bicolor.
Cholera: An intestinal diseases of humans caused by the bacterium Vibrio chlorae. This disease, and typhoid, caused by the bacterium Salmonella typhi, are spread by houseflies, and the Allied forces dusted the whole of Naples with DDT during World War II, in order to prevent major epidemics of insect-borne diseases, including malaria.; DDT-resistant houseflies soon appeared and this was the first known example of the breakdown of an unstable, synthetic pesticide to new strains of the pests. It was this failure of DDT that initiated the ‘boom and bust cycle’ of pesticide production.
Chromosome: Microscopic, threadlike bodies that occur in the nuclei of plant and animal cells. Each chromosome consists of strands of DNA, which is the protein that encodes all genetic information. This information is made up of units called genes.; Chromosomes occur in pairs, with one of each pair coming from the male parent, and one from the female parent. Each gene normally consists of two alleles, with one on each of the pair of chromosomes.; During the process of cell division, the pairs of chromosomes replicate in a process called mitosis. When gametes are produced, the pairs of chromosome separate, without replication, to form two haploid gametes. A chromosome is the most concentrated known system of storing information.; Bacteria and viruses do not store their genetic information in chromosomes.; See also: diploid, doubled monoploid, tetraploid, etc.
Chrysanthemum cineriifolium: The species of daisy, called pyrethrum, from which natural pyrethrins are extracted. Pyrethrum originated in Dalmatia (the area that used to be called Yugoslavia) where people still put dried pyrethrum flowers in their bedding to kill fleas and bed bugs.; They have apparently been doing this for centuries, without any resistant fleas or bed bugs appearing, demonstrating that natural pyrethrins are a stable insecticide. But this insecticide is currently too expensive for widespread use in crop protection.; Pyrethrum is open-pollinated and is an excellent crop for amateur breeders. The breeding objectives should be both a high yield of flowers, and a high pyrethrin content in those flowers. The latter can be professionally assessed in a commercial or university laboratory, or an amateur bioassay can be obtained by adding a minimal amount of powdered, dried, flower to a jam jar containing an insect such as a housefly.; Some agricultural engineering will also be required in order to produce a mechanical harvester. If the price of pyrethrins could be reduced significantly, the crop protection market would be virtually unlimited. This is thus a crop of great potential. See pyrethrins for a description of the insecticide itself.
CIAT: Centro Internacional de Agricultura Tropical. This is the international research centre for tropical agriculture located in Cali, Colombia. It is one of the CGIAR research stations.
Cicadulina spp.: Species of leaf hopper insects. Some species are vectors of virus diseases of plants, the most notable being maize streak virus in Africa.
Cicer arietinum: Known as chick pea, or gram, this is the most important pulse in India, particularly in the semi-arid areas, as it is very resistant to drought.; This plant is self-pollinating and, because the pods contain only one or two seeds, cross pollination by hand is a laborious business. Apart from this, it is a suitable crop for amateur breeders, especially in India where many local landraces offer scope for screening.; There is need for improved horizontal resistance to a number of diseases, and to the gram caterpillar, Heliothis armigera. Storage pests are a serious problem and the possibility of developing horizontal resistance to them merits investigation.; This is a crop that has extinct wild progenitors.
Cichorium spp.: C. intybus is chickory, whose dried and roasted roots are used for blending with coffee. The young shoots of C. endiva are endives, and are used as a vegetable, mainly in salads.
Cimex lectularius: A flat, wingless, reddish-brown, hemipterous bug, known as the bed bug, of interest in that the natural pyrethins in Chrysanthemum cineriifolium have remained a stable insecticide after centuries of use in Dalmatia.
CIMMYT: Centro Internacional de Mejoramiento de Maiz y Trigo. Located near Texcoco, in Mexico, this is the home of the miracle wheats, and tends to use pedigree breeding and single-gene resistances.; CIMMYT and IRRI are examples of autocratic plant breeding, as opposed to the democratic plant breeding of plant breeders associations like the Open Plant Breeding Foundation.; This is one of the CGIAR research stations.
Cinchona spp.: Several species of this South American genus of trees are cultivated for the extraction of quinine and other drugs.
Cinnamomum zeylanicum: The spice cinnamon, consists of the dried green bark (called quills) of an open-pollinated, evergreen tree, which is indigenous to Sri Lanka (Ceylon), and is propagated by seed.; Selection within existing crops should lead to improved clones and vegetative propagation. There is thus scope for amateur breeders. There are no serious pests or diseases, but these might develop if a single clone is cultivated excessively.; Cinnamon is a very ancient crop and was being shipped by Austronesian people to Madagascar, and from there it was taken to Africa and, eventually, to ancient Rome.; The Portuguese conquered Ceylon in 1536 and gained a monopoly in the cinnamon trade. The Dutch conquered them, and the monopoly, in 1656. Then the British conquered the Dutch, and won the monopoly, in 1796. In the nineteenth century, commercial production commenced in various parts of the world, and the monopoly was broken, but the Sri Lanka cinnamon remains the best.; Distillation of the wood of C. camphora produces camphor.
Cinnamon: See: Cinnamomum zeylanicum.
CIP: Centro Internacional de la Papa. Located in Lima, Peru, this is the international research centre for potatoes. This is one of the CGIAR research stations.
Circadian rhythm: Most living organisms have a twenty-four hour rhythm in various of their metabolic processes. This ‘circa-diem’ rhythm is apparently controlled by an internal biological clock which continues to function under artificial conditions of continuous day or night. However, the mechanism of this clock is not yet understood.
Citrullus lanatus: Water melon. This is a member of the Cucurbitaceae family, and is a native of Africa. Like all cucurbits, water melons are open-pollinated and there is great variation in all the quality characteristics. There are a number of pests and diseases and amateur breeding for horizontal resistance is likely to be productive.
Citrus (generally): Citrus are among the oldest fruits, originating mainly in S.E. Asia, and having spread throughout the Old World in antiquity. They are some of the most popular fruits, usually eaten fresh, but also made into special jams known as marmalade. They are a major source of Vitamin C.; Citrus spp. are members of the botanical family Rutaceae. Most citrus trees are grafted on to stocks that are resistant to various root rots, but graft incompatibilities can lead to secondary problems, such as stem-pitting due to the tristeza virus. Citrus fruits become orange or yellow when ripe but, in the tropics, they may remain green.; Many citrus species produce nucellar (i.e., parthenocarpic) seeds. The rind of most citrus fruits contains essential oils that are used in a wide range of perfumes, soaps, and foods.; Most citrus varieties are so popular, and so well entrenched, that there is little scope for amateur breeders to produce improved quality. There is scope for improved horizontal resistance, but amateur breeders should regard this as one of the more challenging crops.
Citrus aurantifolia: Lime. In the late eighteenth century, the British admiral Nelson insisted on his sailors drinking lime juice, in order to prevent scurvy, which is due to a deficiency of Vitamin C. This earned the British the nickname of ‘limeys’. Lime fruits do not travel well and are little used in temperate countries. However, they are very popular in tropical and subtropical countries where the fresh juice is routinely squeezed over food and into alcoholic drinks.
Citrus aurantium: The sour or Seville orange. Not suitable for eating as fresh fruit, these oranges are used mainly for making marmalade. Sour orange is also widely used as a rootstock for other species of citrus, but these graft combinations are often susceptible to the Tristeza virus. This species includes the Bergamot variety that yields Bergamot oil, which provides the characteristic flavour of Earl Grey tea.
Citrus limon: Lemon. This is the origin of the term ‘lemonade’ and this yellow fruit has always been popular in temperate countries where limes were unavailable. It is usually too sour to be eaten as a fruit, but it is widely used as a flavouring and garnish in many foods and drinks. The freshly grated peel, known as zest, is also widely used as a flavouring.
Citrus paradisi: Grapefruit. Now popular as a breakfast dish, this mildly bitter, acidic fruit is one of the largest citrus fruits. It is of relatively recent origin and is thought to be a chance hybrid between two other Citrus spp. The name ‘grapefruit’ was apparently used for the first time in Jamaica in 1814, but its etymology is obscure.
Citrus reticulata: Mandarin, or tangerine. Often known as the ‘loose-skinned’ oranges because of their easy peeling, these fruits are used mainly as a dessert. They probably originated in Vietnam and are of ancient cultivation in China and Japan.
Citrus sinensis: Sweet orange. This is the most important of the citrus fruits, in terms of acreage, and it is now used mainly as a fresh juice at breakfast in order to provide a daily dose of Vitamin C.; There are three main types of cultivar. Navel oranges have a second row of carpels opening at the apex with the appearance of a ‘belly button’ or navel. Blood oranges have a red, or streaky red pulp. Thirdly, there are cultivars with normal fruits.; ‘Valencia’ is the most important commercial cultivar, followed by ‘Washington Navel’ and ‘Jaffa’.
Claviceps purpurea: The fungus that causes ergots and ergotism. The fungus infects the stigma of an open-pollinated cereal, such as rye, or various species of open-pollinated fodder grasses. The seed is then transformed into a black fungal body that is the ergot and is poisonous.; Ergotism used to be a serious problem in the rye districts of eastern Germany, Poland, and western Russia, where wheat is difficult to grow. This problem was largely solved by the introduction of potatoes, which became the staple food of these areas.; Rye ergots are a source of the lysergic acid that is used in the production of LSD.
Clay: 1. Clay minerals are kaolin, mica, talc, and similar groups.; 2. Clay is a component of soils, with a particle size of less than two microns.; 3. Clay soils contain at least 20% clay particles and are described as heavy soils.
Cleaning crop: A crop, such as potatoes, that is used in the rotation to help suppress weeds. It does this by shading out the young weeds, which can be finally destroyed by cultivation.
Cleistothecium: (Plural: cleistothecia). The entirely enclosed body containing one or more asci, typical of the Erysiphales. The cleistothecium is ruptured by the developing ascus which can then eject its ascospores.
Cline: A large population covering a wide geographic area and exhibiting genetic change from one end to the other. For example, wild cocoa occurs as a cline covering the length of the Amazon River, with totally allogamous types at the river source, in the West, and a gradual change to autogamous types at the river mouth, in the East.
Clone: A population in which all the individuals are descended by asexual reproduction from one parent individual. Consequently, all the individuals within a clone are genetically identical. However, some clones may contain asexually produced variants called ‘sports’ or mutants.; Vegetative propagation of plants includes the use of grafts, cuttings, suckers, tuber, bulbs, corms, setts, and rhizomes.; Typical clonal crops are potatoes, sweet potatoes, yams, cassava, strawberries, hops, apples, olives, citrus, dates, sugarcane, bananas, and pineapples.
Clove: See: Eugenia caryophyllus.
Clovers: See: Trifolium spp.
Cluster bean: See: Cyamopsis tetragonolobus.

Glossary: Co-Cz

Cobnut: See: Corylus avellana.
Coca: See: Erythroxylon coca.
Cochliobolus: See: Helminthosporium.
Cocoa: See: Theobroma cacao.
Coconut: See: Cocos nucifera.
Cocos nucifera: The coconut palm. An extraordinarily useful palm that provides food, drink, fibre, timber, thatch, mats, fuel, and drinking cups.; This palm is also the source of copra, the dried endosperm, which was the major source of vegetable oil until the mid-twentieth century, and the major cash crop on innumerable tropical islands. This oil was used mainly for the manufacture of soap, and the market declined with the development of soapless detergents and other oil crops, such as soya, canola, and oil palm.; The species is usually divided into tall palms and dwarf palms. It is thought that the former represent the wild type, and the latter are the result of very ancient domestication that brought more numerous nuts closer to the ground and easier to open.; There is scope for amateur breeders to cross-pollinate the two types to produce hybrid palms with an increased yield and, in the Caribbean, resistance to lethal yellowing disease.; The coconut is of considerable anthropological interest because it provided a source of both drinking water and Vitamin C on long ocean voyages. Austronesian people were sailing across oceans several millennnia before the Chinese developed ocean-going ships in the fourteenth century, or the Europeans, in the fifteenth century. This ocean travel permitted the colonisation of uninhabited ocean islands, and the spread of the Austronesian family of languages to Madagascar in the West, Easter Island in the East, Hawaii in the North, and New Zealand in the South.; Coconuts spread naturally, by floating on sea water, to the east coast of Africa, and the islands of the Western Pacific. However, they were unable to reach the west coasts of America, or the Atlantic. They were taken to both areas by European sailors in the sixteenth century. The Portuguese took them from East Africa to West Africa and the Caribbean. The Spanish took them across the Pacific to the New World.; The palms of the west Pacific were in epidemiological contact with the centre of origin, and were resistant to various coconut diseases. The palms of East Africa, however, had been separated epidemiologically from the centre of origin for millennia, and they are susceptible to diseases such as Cadang-Cadang in the Philippines, and Lethal Yellowing in the Caribbean.; Both diseases can be controlled by planting hybrids that are crosses between the Pacific Tall and the dwarf palms.
Coco-yam: See: Xanthosoma sagittifolium and Colocasia esculenta.
Codling moth: See: Carpocapsa pomonella.
Coffea arabica: Arabica coffee. This is the main coffee of commerce. It is an autogamous allotetraploid, (2n = 44) believed to have been derived from an infertile cross between the two wild diploid, Coffea canephora and Coffea eugenioides (2n = 22), which subsequently doubled its chromosome number to become a fertile tetraploid.; First cultivated in Ethiopia, it was taken to Arabia Felix (Southern Yemen) where the famous Mocha variety was grown. The Dutch then took it to Ceylon (Sri Lanka) and Indonesia. Seed was then taken to Amsterdam, and one tree was given to the King of France who sent seed to Martinique. All the coffee of the New World was derived from this seed and was a pure line. All the pests and diseases had been left behind in the Old World, and Latin America soon became the principle coffee producing area, with Brazil in the lead.; As a result of a horizontal resistance program, Ethiopia now has coffee cultivars with sufficient resistance to control all the major pests and diseases, including coffee berry disease, and it is the only country that can produce this resistant coffee that does not need any crop protection chemicals.; In countries where the ripe berries are picked by hand, the ‘wet method’ of processing is used. The coffee is pulped, graded, and fermented to produce so-called parchment coffee, which is then dried in the sun. It is then hulled to remove the parchment and silver skin. This produces a mild coffee that will tolerate a light roast.; With the ‘dry method’, whole cherries are dried in the sun and then milled. This produces a hard coffee which must be given a dark roast.; Possibly the most promising approach to coffee breeding is to re‑create the allotetraploid from the two wild diploids. But this is not recommended for amateur breeders.; See also: Hemileia vastatrix.
Coffea canephora: Robusta coffee. Less desirable than C. arabica, it is suited to a much wetter climate, and is in demand for the manufacture of instant coffee. Believed to be one of the diploid parents of the allotetraploid Coffea arabica.
Coffea eugenioides: A wild diploid coffee of eastern Africa, of no commercial value, but it is believed to be a parent of the allotetraploid Coffea arabica. If an attempt were made to re-create Coffea arabica, this species would become scientifically important.
Coffee: See: Coffea arabica, Coffea canephora, and Coffea eugenioides.
Coffee berry disease (CBD): See: Colletotrichum coffeanum.
Coffee leaf rust: See: Hemileia vastatrix.
Coix lachryma-jobi: Adlay, or Job’s tears. Coix is a genus of monoecious grasses. Several species are of ancient cultivation as cereals in S.E. Asia, China, and Japan. A crop of considerable potential for amateur breeders.
Cola: See: Cola spp.
Cola spp.: Several species of this West African genus provide kola nuts that are rich in caffeine and are chewed as a stimulant. In ancient times, the kola trade defined the camel caravan routes from Sokatoo and Timbuctoo to the Mediterranean. There is now no international trade in kola nuts, and modern cola drinks contain no true kola.
Colchicine: A drug extracted from meadow saffron and used to induce polyploidy in plants.
Colletotrichum coffeanum: This is quite the most serious disease of coffee, and it is caused by the fungus Colletotrichum coffeanum. At present it is confined to eastern Africa.; The fungus resides in the bark and parasitises the berries only. In a susceptible tree, there is a total loss of all berries several months before harvest, and this represents the minimum level of horizontal resistance.; In resistant trees selected recently in Ethiopia, there is no loss of berries, and this represents the maximum level of horizontal resistance. In other countries where the disease occurs, it is controlled with fungicides.
Colocasia esculenta: This vegetatively propagated root crop is known variously as taro, dasheen, or coco yam. It is one of the aroids, and was the basis of the agriculture in Papua New Guinea, which is amongst the oldest in the world, dating from about 7000BC.; It is a labour-intensive crop, and it became only a minor staple, which lacked the potential of a major staple, capable of supporting the growth of cities and the development of a sophisticated civilisation. There is some room for improvement by amateur breeders, mainly by selection within existing cultivar.
Colorado potato beetle: See: Leptinotarsa decemlineata.
Combine harvesting: Harvesting grain with a self-propelled machine that both cuts and threshes the crop. Combine harvesters usually have a storage bin that can be discharged into a truck moving alongside, while the harvesting continues without a break. Many machines also have a system of chopping the straw and discharging it on to the ground, often in windrows suitable for burning to control pests and diseases. Combine harvesters are used on most temperate cereals, some pulses, and crops such as mustard and canola.
Complexity theory: Modern complexity theory divides all systems into the two categories of linear and non-linear systems.; The ‘hard’ sciences, such as chemistry, physics, and astronomy, are based on linear systems, in which the parameters are fixed, are easily measured, and the outcomes easily predicted. The ‘soft’ sciences, such as all the life sciences, are based on non-linear systems, in which the parameters are liable to change, are difficult to measure, and the outcomes difficult to predict.; For example, the solar system is a linear system, and we can predict the phases of the moon, and the tides, with great accuracy for centuries ahead. But the weather is a non-linear system and even short-term weather forecasts can be unreliable.; An essential feature of non-linear systems is the property of self-organisation and this is the basis of the concept of self-organising crop improvement.; See also: General systems theory.
Compositae: The botanical family that includes lettuce, sunflower, Jerusalem artichoke, pyrethrum, safflower, chrysanthemums, and daisies. It is characterised by an inflorescence of many small florets in a single disk, usually surrounded by the petals of the outermost florets.
Compost: Compost is organic matter that has been broken down into humus, mainly by aerobic bacterial decomposition. It is an important resource for organic farmers, as a soil amendment that adds organic matter to the soil and provides high-quality nutrition to their crops.; Source materials for compost can include animal manure and bedding, crop stalks and hulls, food waste, etc. Composting can be done in-field, in compost piles or in windrows.
Comprehensive horizontal resistance: See: horizontal resistance.
Congo pea: See: Cajanus cajan.
Conidia: The asexual produced, microscopic spores of a fungus that permit both vegetative propagation and a rapid and widespread dissemination. Conidia are usually produced in very large numbers, and these fungi are r strategists capable of a rapid and large population explosion.
Conidiophore: The microscopic stalk of a fungus that bears asexual spores called conidia.
Conifer: Any tree of the order Coniferales, usually bearing cones and having needle-like leaves. Known as the Gymnosperms, they include pines, cedars, yew, and redwood.
Conservation: See: Genetic conservation.
Consultative Group for International Agricultural Research: The Consultative Group on International Agricultural Research, is located in Washington, DC.; This is the body that allocates funds, amounting to several hundred million dollars annually, to the International Research Centres.
Consumers: 1. A term in economics: purchasers of market produce. Consumers are a significant factor in the self-organising food production system because they determine which items sell best. For this reason, they are also a significant factor in self-organising crop improvement.; 2. A term in evolution: one of the three primary groups of living organism, the others being producers and reducers. Consumers obtain their nutrients from other living organisms, and they include all herbivores, carnivores, omnivores, and parasites.
Contamination: From the point of view of plant breeders, contamination refers to unwanted foreign pollen that can accidentally enter the recurrent mass selection from outside, and introduce undesirable characteristics such as susceptibility.; Contamination can also occur in cultures of plant pathogens.; A distinction is also made between contaminated seed and infected seed. The former has parasites on the outside and can be decontaminated with surface seed dressings. The latter has internal parasites, which can be eliminated only by hot water treatment, or by systemic chemicals.
Continuity: See: Continuous epidemic.
Continuous distribution: Quantitative data that reveal a continuous spectrum of values between a minimum and a maximum. See also: Normal distribution.
Continuous epidemic: In epidemiology, a continuous epidemic is one in which the parasitism never stops. This is sometimes called endemic disease. The epidemiological significance of continuity is that the parasite does not need to find a means of survival in the absence of a host. (See also: discontinuity).
Continuous pathosystem: A pathosystem in which host tissue is continuously available, and the parasitism continues indefinitely, without a break. Continuous pathosystems occur typically in evergreen, perennial hosts. Auto infection is of primary importance in continuous pathosystems.; Vertical resistance has no survival value in continuous pathosystems, and it is not found in a crop species that is derived from a continuous wild pathosystem.; See also: discontinuous pathosystem.
Continuous variation: A term sometimes used for quantitative variation, in which there is every degree of difference between two extremes. Thus, horizontal resistance shows continuous variation between its minimum and maximum levels. See also: discontinuous variation.
Contour ploughing: A system of ploughing in which the furrows follow the land contours in order to minimise soil erosion.
Copper: Copper is an important plant nutrient. It is an immobile element. Deficiency symptoms show first in the young leaves and shoots and result in general growth failure. Various copper compounds are used as fungicides.
Copper sulphate: Copper sulphate is obtained by dissolving metallic copper in sulphuric acid to produce a blue solution that crystallises into blue crystals known as ‘blue stone’. It is a constituent of Bordeaux mixture, which is made by adding newly slaked lime to a solution of copper sulphate.
Copra: See: Cocos nucifera.
Copyright: The legal protection of intellectual property. Most countries now have a system of granting copyrights to plant breeders for new cultivar. The breeders are then entitled to royalties on all seed sales of their cultivars. This system of reward is of special interest to amateur plant breeders, and to plant breeders associations. New cultivars with high levels of horizontal resistance can be accurately identified with DNA ‘finger printing’.
Coriandrum sativum: An annual herb called coriander, and widely used since ancient times as a seasoning.
Corchorus spp.: Jute. This fibre crop is cultivated mainly in India. It provides considerable scope for amateur breeders, who should remember, however, that plastic fibres have largely replaced the natural plant bast fibres.
Corm: An underground storage organ of a monocotyledon consisting of a solid swollen stem. The next season’s corm usually forms on top of the old one. Not to be confused with a bulb. Crocuses have corms, and tulips and onions have bulbs.
Corn: Technically, any small cereal grain. However, the use of this term is usually confined to the most important cereal within a region. Thus, in the corn belt of the USA, the term refers to maize. Corn in Britain is wheat. In Scotland, it is oats.
Corolla: A whorl, or whorls, of petals that forms the inner envelope of a flower. The petals may be either free or joined, and they are often brightly coloured to attract pollinating insects.
Corporate plant breeding: Plant breeding undertaken by large corporations, usually chemical manufacturers. Because their motives are profit-driven, they have a vested interest in promoting the use of chemical pesticides rather than horizontal resistance. Consequently, they can be expected to produce new cultivars that have excellent yield, quality, and agronomic suitability, but that also have low levels of resistance.; Corporate plant breeding is also involved in genetic engineering and the production of cultivars that have special properties, such as resistance to herbicides.
Corylus avelana: The hazel nut, cobnut, or filbert. This species shows considerable diversity and some taxonomists have suggested additional specific names. Not much scope for amateur breeders.
Corynebacterium: A genus of plant pathogenic, gram-positive bacteria that cause disease in tomato, potato, and various ornamentals.
Cosmopolitan cultivars: Cultivars that have a wide geographical and environmental range.
Cotton: See: Gossypium spp.
Cotyledon: The first leaves produced by germinating seeds are called cotyledons. All flowering plants (Angiosperms) are divided in those that produce either one or two cotyledons at the time of seed germination.; Monocotyledons are plants that produce a single cotyledon, and they are often called the narrow-leaved plants. Among cultivated plants, they include all the grasses, cereals, and sugarcane, crops of the onion family, bananas, pineapples, palms, and ginger.; Dicotyledons are plants that produce two cotyledons, and they are often called the broad-leaved plants. Seeds of dicotyledons can be split into two halves (e.g., split peas). Among cultivated plants, they include all the peas and beans, most of the temperate fruits and nuts, crops of the cabbage, cucumber, and potato families, cotton, rubber, tea, coffee, cocoa, cassava, sweet potato, and many vegetables and herbs.
Covered smuts: The smut fungi are a group within the Basidiomycetes which cause diseases mainly in cereals and grasses. The covered smuts (c.f., loose smuts) are so-called because they form a black spore mass inside the seed, and these spores are released when the seed coat breaks. In cereal crops, this produces contaminated seed, as opposed to infected seed, and the disease can be easily controlled with a fungicidal seed dressing.; There is a covered smut of barley (Ustilago hordei), oats (Ustilago kolleri), and sorghum (Sphaceolotheca sorghi). The covered smuts of wheat are usually called bunt, or stinking smut, and are caused by Tilletia caries, T. foetida, and T. contraversa.
Cowpea: See: Vigna unguiculata.
Cranberry: See: Vaccinium spp.
Crescentia cujete: The calabash, which is native to tropical America. The hard fruits are used as containers and musical instruments (maracas).
Cress: See: Lepidium sativum.
Crinipellis perniciosa: The fungus which causes ‘witches’ broom’ disease of cocoa.
Crocus sativa: Saffron. A much prized spice and yellow colouring obtained from the stigmas of the Crocus. Saffron is the basis of French bouillabaisse, Spanish paella, English saffron buns, Jewish gilderne, Russian challah, Indian zaffrani chawal, and Persian sholezard.; Saffron is also the most expensive spice of them all, because the stigmas of a crocus flower are the most labour-intensive of all crops to harvest.; The wild progenitors of the saffron crocus are extinct, and this is an indication of its antiquity. Like garlic, the cultivated crocus does not set seed, and, it can be propagated only by corms. Multiplication of the crop is a very slow process because only two or three new corms are formed each year at the base of the old corm.; It is not known how many clones exist but it is quite clear that all of them are ancient, and that they have been cultivated for millennia without any use of crop protection chemicals.; Not recommended for amateur breeders.
Cronartium ribicola: White pine blister rust. This is a heteroecious rust of five-needled pines (Pinus spp.), and its summer host is Ribes spp. It was apparently introduced to North America at the turn of the nineteenth century, where it largely destroyed the white pine forests.; It is thought (but not proved) that this introduction was an allopatric pathotype native to Eurasia, and that a local, North American pathotype had been present all the time. The two pathotypes would have become isolated from each other some sixty five million years ago with the separation of the continents. This would explain why an apparently functioning gene-for-gene relationship exists in the North American pathosystem of the Eurasian pathotype.; Apparently, the same gene-for-gene relationship exists in both geographical areas and, if confirmed, this would provide a useful indication of the evolutionary age of gene-for-gene relationships. The North American white pines would have had adequate horizontal resistance to their own horizontal pathotype, but not to the allopatric pathotype.; Surviving white pines are likely to be resistant, and their selection and propagation would form an excellent project for a plant breeding club in the forestry department of a university.
Crop: Any population of plants that is cultivated by a farmer. Crops are often defined by their ultimate purpose. Thus, cash crop, subsistence crop, food crop, fodder crop, etc.
Crop architecture: The shape of crop plants and, hence, the nature of the crop itself.; For example, the bean varieties of one species may have either the determinate habit, or they may be climbing vines. The latter are useful for climbing up maize plants in mixed cropping, while the former are more suitable as a pure stand, and for mechanical cultivation and harvesting.; The miracle wheats and rices of the Green Revolution are dwarf varieties that can tolerate high rates of nitrogenous fertiliser without lodging.; Soybeans became an important commercial crop only after types suitable for combine harvesting had been developed.; Some crops, such as potatoes, can be densely planted in order to cover the ground completely, in order to control weeds.
Crop husbandry: The practice and science of the cultivation of crops.
Crop loss due to parasites: The crop losses caused by parasites are usually subdivided into pre-harvest and post-harvest losses, also known as field losses and store losses, respectively.; Pre-harvest losses are controlled primarily by breeding the host for resistance, and by the use of crop protection chemicals. Other methods include rotation, to reduce the incidence of soil-borne parasites, and the burning of crop residues.; Post-harvest losses are controlled mainly by keeping the product dry, and by depriving the parasites of oxygen.
Crop parasites: Any organism in which an individual spends a major proportion of its life cycle inhabiting and obtaining nutrients from one host individual.; The term includes parasitic Angiosperms, insects, mites, nematodes, fungi, bacteria, phytoplasmas, viruses, and viroids.; Entomologists normally handle the insects and mites, while plant pathologists usually handle all the other categories.
Crop pathosystem: An agricultural plant pathosystem in which people have changed the natural mechanisms of self-organisation. The host, the parasite, and the environment have all been altered by the activities of agriculture.; A crop pathosystem is normally characterised by genetic uniformity, and genetic inflexibility.; If it is derived from a continuous wild pathosystem, it will not have any vertical resistances; if derived from a discontinuous wild pathosystem, it may have vertical resistances.
Crop protection: The combined disciplines of entomology, plant pathology, and plant breeding, aimed at jointly and cooperatively reducing crop losses resulting from both parasites and weeds.; Most modern crop protection depends very heavily on crop protection chemicals, and the chief goal of amateur plant breeders is to reduce human dependence on chemicals by breeding crops for horizontal resistance.
Crop protection chemicals: In the wide sense, this term means any chemical used to control crop parasites or weeds. The former are mainly insecticides and fungicides, while the latter are herbicides. In any discussion of crop parasites, however, the term is usually used to exclude herbicides.
Crop protection, natural: As an alternative to synthetic crop protection chemicals, farmers and gardeners may use more natural alternatives such as rotenone, pyrethrin and Bordeaux mixture.; However, organic growers aim to promote a balanced local ecology that minimizes the impact of any one pest or disease, reducing the likelihood of needing to apply crop protection.; See also: integrated pest management.
Crop rotation: The cultivation of a succession of different species of crop on the same land. The main purpose of rotation is to reduce or prevent the build up of large populations of parasites, particularly soil-borne parasites. Other functions include maintaining high levels of soil fertility.
Crop science: The combined disciplines of agronomy, horticulture, plant pathology, entomology, plant breeding, and plant physiology. Agricultural engineering and agricultural economics are sometimes included in this term.
Crop vulnerability: A crop is vulnerable if it is susceptible to a foreign parasite which is absent from the area in question. If the foreign parasite arrives in that area, the susceptibility is revealed, and the vulnerability is manifested. Potential damage then becomes actual damage.; Some crop vulnerabilties are slight and unimportant. Others can be extreme, and the resulting damage can have major social and economic consequences. Thus the potato crops of Europe before 1845 were highly vulnerable to the blight fungus Phytophthora infestans. Note that a crop is vulnerable only if the parasite in question has epidemiological competence in the area concerned.
Cross: Short for cross-pollination.
Crossing generation: In recurrent mass selection, a plant breeding cycle may involve several generations. The crossing generation is the one in which cross-pollination occurs.; See also: single seed descent; late selection; family selection.
Cross-pollination: Fertilisation with pollen coming from a different plant. When cross-pollination involves two genetically different plants, it leads to heterozygosity.; See also: allogamy, outbreeder, self-pollination.
Crotalaria juncea: Sunn hemp, which is cultivated throughout the tropics as a fast-growing green manure. It is also widely used in India as a fibre for sacking and cords, but it is inferior to true hemp (Cannabis).
Cryptic error: The term originally used by J.E. Vanderplank to describe inter-plot interference or parasite interference.
Cucumber: See: Cucumis sativus.
Cucumis anguria: The West Indian gherkin. These fruits are used mainly in pickles, but they should not be mistaken for the more common gherkin which is only a small cucumber.
Cucumis melo: Melon. This highly variable species consists of four basic types, which interbreed freely.; The ‘Cantaloupe’ melon is the most commonly cultivated and is characterised by a think, rough rind.; The ‘Honey Dew’ melon, with ivory skin and green flesh, is also widely grown, and is in the group known as the winter or ‘Casaba’ melons.; ‘Musk melon’ is popular in the United States and has a smooth skin and shallow ribs.; Melons are open-pollinated. Most musk melons are andromonoecious, while Cantaloupes are usually monoecious. A good crop for amateur breeders.
Cucumis sativus: Cucumbers and gherkins. This species originated in India.; There is a wide range of cultivars. The so-called ‘English’ cucumber has long fruits that are used mainly in salads and sandwiches. Pickling cucumbers have small fruits and are pickled as gherkins. The ‘Sikkim’ cucumber of India has reddish-brown fruits.; All members of this species are monoecious, annual herbs, and some are parthenocarpic. There is considerable scope for recurrent mass selection by amateur breeders.
Cucurbita maxima: The pumpkin, also known as the winter squash. This species has extremely large fruit that is widely used for making Jack-o’-lanterns at Hallowe’en. The fruit and seeds are edible. The species is monoecious and can be a fun crop for amateur breeders.
Cucurbita pepo: The vegetable marrow, or squash, which originated in Central America.; This species formed one of the kingpins of ancient Aztec farming, in which maize, beans, and squash were grown in a system of mixed cropping that both supplied a remarkably complete diet, and has proved remarkably sustainable. However, this system is quite labour-intensive.; This species is a very variable, monoecious, annual herb. Most modern breeding has involved pedigree breeding with transfers of vertical resistance genes, and the production of hybrid varieties.; In Europe, the seed is used as a source of high quality oil, and a mutant, lacking the heavy seed coat, produces seed containing 45-50% oil.; There is scope of recurrent mass selection by amateur breeders.
Cucurbita spp.: This genus originated in the area of Mexico-Guatemala and has twenty-six species, of which five are cultivated.; The principle cultivated species is Cucurbita pepo, and is described separately. In addition C. moschata, C. maxima, C. ficifolia, and C. mixta provide winter squash in Central America and parts of South America.; They provide scope for recurrent mass selection by local plant breeders associations.
Cucurbitaceae: The botanical family that includes cucumbers, pumpkins, melons, etc. Most species are open-pollinated, and many are monoecious, and provide scope for amateur plant breeders.; The main cultivated species are the wax or white gourd (Benincasa hispida) used as a vegetable in S.E. Asia; the water melon (Citrullus lanatus); the west Indian gherkin (Cucumis anguria); the melon (Cucumis melo); the cucumbers and gherkins (Cucumis sativus); the pumpkin (Cucurbita spp.); the marrow (Cucurbita pepo); the bottle gourd (Lagenaria siceraria); the loofah (Luffa spp.); the bitter gourd (Momordica charantia); and the choyote or christophine (Sechium edule).
Cucurbits: Members of the botanical family Cucurbitaceae.
Cultigen: A plant species or variety that is known only in cultivation. See also: cultivar; extinct wild progenitors.
Cultivar: A cultivated variety, which has originated and persisted under cultivation, as opposed to a botanical variety, which is a component of a wild species.; Cultivar names should be written with capital letters and enclosed in single quotation marks (e.g., ‘Russet Burbank’), but some authors prefer to use italics without quotation marks.; A cultivar is usually a pure line, a clones, or a hybrid variety, and it is genetically uniform, and genetically inflexible. A cultivar consequently cannot respond to selection pressures during cultivation.; See also: ecotype, agro-ecotype, landrace, micro-evolution.
Cultivation: The various processes of growing a crop.
Culture: In an agricultural context, this word means the growing of either a crop, or a micro-organism.
Cuminum cyminum: Cumin. A member of the botanical family Umbelliferae, cultivated in S.E. Europe, North Africa, India, and China. The seeds are used for flavouring curry powder and other mixed spices.
Curcuma domestica: Turmeric. This genus is native to S.E. Asia and is a member of the ginger family, Zingiberaceae. The rhizomes provide a yellow dye, and a flavouring essential to all curry powders.; It is one of those crops in which true seeds are not produced, and its ancient clones are a useful example of the durability of horizontal resistance. The wild progenitors are extinct.; Various clones exist in India, usually named after their home district, and varying in their suitability as a spice or a dye.
Currants: In a horticultural sense, currants are species of Ribes, and are known as red, white, and black currants. The black currant is a useful source of Vitamin C. However, the currants used in currant buns, and other cooking, are a special variety of dried grape called ‘Corinth’, and the term ‘currant’ is a corruption of this name.
Curry powder: In India, any good cooks make their own curry powders, and there are as many recipes as there are good cooks.; Most curry powders contain about 25% turmeric (Cucurma domestica), 25% coriander (Coriandrum sativum) seeds, and various amounts of cumin (Cuminum cyminum) seeds, cardamoms (Elettaria cardomomum), fenugreek (Trigonella foenum-graecum) seeds, chillies (Capsicum annum), ginger (Zingerber officinale), black pepper (Piper nigrum), and dill (Anethum graveolens) seeds.
Cuscuta spp.: Dodder, also known as strangle-weed, hellbind, hailweed, and devil’s hair. These species belong to a mono-generic family, the Cuscutaceae, in which all members are parasitic on other plants.; Dodder consists mainly of yellow-red, slender, vine-like stems with vestigial leaves, and the plants lack chlorophyll entirely. Dodder can occasionally be an agricultural nuisance.; Dodder is used in research to transmit viruses from one host plant to another.
Cuticle: The outermost layer of the epidermis. A thick cuticle is often a mechanism of resistance.
Cuttings: Pieces of stem that are planted so that they may form roots and, eventually, new plants by vegetative propagation. All the cuttings originating from a single parent constitute a clones. The best method of rooting cuttings is in a mist-propagator.
Cyamopsis tetragonolobus: The cluster bean, or guar, is a member of the Leguminosae. Its wild progenitors are extinct but it is thought to have been a native of Africa, taken at an early date to S.E. Asia, where it now has many uses. It is also grown as a cash crop in Texas and Oklahoma. Some scope for amateur breeders in S.E. Asia.
Cyanide: Any of the extremely poisonous salts of hydrocyanic acid, particularly potassium cyanide. It was used as an insecticide before the discovery of DDT and later synthetic insecticides.
Cyano-bacteria: Also called the blue-green algae, these prokaryote organisms contain photosynthesising pigments. They were apparently the first producers to appear on the evolutionary scene, and they have survived until the present.
Cyclone separator: Equipment for separating dust or other fine particles from air. The dusty air is spun as a cyclone inside a hollow cone. Being heavy, the solid particles are thrown against the sides of the cone by centrifugal force, and they sink to the calm air at the bottom of the cone. The clean air escapes through the top of the separator.; This equipment is usually quite large, and handles large quantities of dusty air being extracted from a factory or mill. However, miniature versions are made for collecting relatively large quantities of microscopic pollen grains, rust spores, etc.
Cynara scolymus: The globe artichoke. This Mediterranean crop is a perennial thistle and is vegetatively propagated, because true seedlings are very variable.
Cynodon dactylon: Star grass, also known as Bermuda grass or Bahama grass. One of the most widely dispersed grasses in the tropics and subtropics, extending even to S.W. England.; While it can be a serious weed, with fast-growing rhizomes and runners, it can be useful as both a pasture grass and a turf grass. It is usually propagated vegetatively, but some forms can be sown by seed.; Non-rhizomatous, high-yielding strains are known and are very useful. There is scope for amateur breeders.
Cyphomndra betacea: The tree tomato. This tree is not a true tomato but it belongs to the same family (Solanaceae) and it has fruits that taste like tomatoes.
Cyrtosperma chamissonis: Giant taro. This plant is a huge herb growing up to four metres in height, grown for its tubers that take several years to mature, with a record of a sixty kilogram tuber in a plant ten years old. It is propagated vegetatively and it is usually grown in swamps.
Cytoplasm: The contents of a cell that are enclosed by the membrane, but excluding the nucleus.

Glossary: D

Dactylis glomerata: A pasture grass grown mainly in the temperate regions of the Old World.
Daktulosphaira vitifoliae: The new scientific name for Phylloxera vitifoliae of grapes.
Damping-off: A disease of very young seedlings, which rots the stem at the soil surface. Affected seedlings then fall over like miniature, felled trees.; The disease is caused by fungi such as Phytophthora, Pythium, and Rhizoctonia, and it is greatly aggravated by over-watering, which should be avoided. Otherwise, the best methods of controlling the disease are to use soils that have either been pasteurised with steam heat, or treated with a fungicidal soil drench.
Dandelion: See: Taraxacum.
Darwin, Charles: The English discoverer of evolution, Charles Robert Darwin (1809-82) was appointed to the post of naturalist on the scientific expedition of HMS Beagle (1831-6). In 1842, he bought Down House, in Kent, where he lived for the rest of his life, apparently suffering from Chagas disease, which he had contracted in South America.; Having a private income, he could investigate as he pleased and at his own slow pace. By 1844 he had developed his theory of evolution but he delayed publication until a note from Alfred Wallace revealed his independent discovery of the same idea.; In 1858, their joint paper was read to the Linnaean Society and, in 1859, Darwin published his famous book On the Origin of Species by Means of Natural Selection. The book was widely and quickly recognised, but opposition came from religious groups who preferred a literal interpretation of the Bible.
Dasheen: See: Colocasia esculenta.
Date palm: See: Phoenix dactylifera.
Daucus carota: The carrot. This is an open-pollinated member of the family Umbelliferae and the production of uniform lines is difficult. Some work has been done on hybrid varieties but there are technical problems with this approach.; There is plenty of scope for the accumulation of horizontal resistance, but amateur breeders should be a little wary of tackling this crop.
Day-length: A parameter that governs the initiation of flowering and other developments in plants.; Tropical plants are often short-day plants (e.g., potatoes that will not form tubers until the September equinox when grown in temperate regions) and temperate plants are often long-day plants (e.g., hops and olives which will not flower in the tropics).
Day-neutral: A day-neutral plant is one that is not affected by day-length (e.g., temperate cultivar of potato). See also: photoperiod-sensitive.
DDT (Dichloro-diphenyl-trichlor-ethane): One of the dirty dozen chemicals called POPS (persistent organic pollutants). The first, most famous, most successful, and most notorious of the synthetic insecticides.; It was first synthesised chemically in 1873 but its insecticidal properties were not discovered until 1939, by the Swiss entomologist Paul MÃ¼ller, who was awarded the 1948 Nobel Prize in Medicine.; DDT proved to be of enormous value in the control of insect vectors of human diseases, such as malaria, typhoid, and cholera. Scientists still speculate whether DDT or penicillin has saved the most human lives.; DDT also controlled the vectors of many animal diseases, as well as numerous crop pests. The latter included major pests such as Colorado beetle of potato, boll worms of cotton, and codling moth of apples. It should be remembered that these pests had previously been treated with compounds of lead, arsenic, mercury, and cyanide.; DDT was both cheap and persistent. The peak production in the USA was in 1961 when 175 million pounds were produced. However, its widespread abuse led to serious environmental damage and fears for human health.; Because DDT is water-insoluble, but fat-soluble, it accumulates in body fat, and a phenomenon called biomagnification leads to increasing concentrations of DDT up the food chain. Humans, as well as many carnivorous birds are at the top of their food chains and accumulate the highest levels.; A further problem was the development of DDT-resistance in target insects. This was the first example of an unstable insecticide.; Another problem concerned the killing of non-target and beneficial insects, such as pollinating bees, and the agents of biological control.; In 1973, its use in the USA was banned, and many other countries followed this example. It is now banned by international treaty except in areas where its use is essential for the control of malaria.
Death: In systems terminology, death is a loss of behaviour, while decay is a loss of structure. Life is an emergent property, and death is the irrevocable loss of that emergent.
Death rate: The rate at which a population is losing individuals.; When the death rate is constant, and equal to the birth rate, the population size does not change. When the death rate exceeds the birth rate, the population growth is negative, and the population size declines. But when the birth rate exceeds the death rate, the population growth is positive, and the population size increases.; When the positive population growth is very rapid, and it is called a population explosion. This rapid rate is typical of râ€‘strategists.
deBary: The German botanist Heinrich Anton deBary (1831-88) is considered the founder of modern mycology.
Deccan hemp: See: Hibiscus cannabis.
Deciduous: The habit of some trees and shrubs of shedding their leaves, by abscission, at the end of each growing season. The function of this habit is usually to escape an adverse season, such as a winter, or a tropical dry season.; The deciduous habit also has advantages in the control of leaf parasites by providing a discontinuous pathosystem in which a gene-for-gene relationship can operate as a system of biochemical locking.; Most deciduous trees are Angiosperms. See also: n/2 model, Seasonal tissue.
Deficiency diseases: Deficiency diseases are among the non-parasitic physiological disorders, which are due mainly to nutritional deficiencies or toxicities. Each nutritional element produces its own deficiency symptoms.; Within one plant, mobile elements can be taken from old tissues to feed the young tissues, and the symptoms then appear mainly in the older tissues. Conversely, immobile elements cannot be re-allocated in this way, and the main deficiency symptoms then appear in the youngest tissues.; Deficiency symptoms are easily confused with herbicide injury, and a specialist should usually be consulted.; For the symptoms of each mineral deficiency, see Nitrogen, Phosphorus, Potassium, Magnesium, Calcium, Boron, Sulphur, Iron, Zinc, Copper, and Manganese.
Defoliation: Loss of leaf. Defoliation can be:; 1. natural, as with leaf-fall in a deciduous tree or shrub;; 2. pathologically induced by the activities of parasites;; 3. induced by the misuse of herbicides; or; 4. from abnormal environmental conditions, such as severe drought.
Dehiscent: This term means that a seed capsule, anther, etc, opens spontaneously when mature.
Democratic plant breeding: The converse of autocratic plant breeding. With democratic plant breeding, as many breeders as possible are producing as many cultivars as possible so that the farmer has a wide choice of cultivars.; This approach is possible with the use of horizontal resistance because breeding for this kind of resistance is so easy. In many cases, farmers can do their own plant breeding.; Once there are enough amateur plant breeders, the whole system of crop improvement will become self-organising.
Density-dependent selection: The limiting of the size of a population (e.g., a vertical pathotype) by mechanisms that are also controlled by the size of population.; This is a probable genetic mechanism for controlling the system of locking of the n/2 model, ensuring that all the n/2 biochemical locks and keys occur with an equal frequency.; The rarity of a vertical pathotype or pathodeme is a reproductive advantage that leads to commonness. And commonness is a reproductive disadvantage that leads to rarity.
Derris elliptica: The powdered dried root of this leguminous plant contains rotenone and other toxic compounds that are used as an insecticide and a fish poison in S.E. Asia.; The insecticide is used mainly as a hair wash to control lice. This derris insecticide is stable, as no derris-resistant strains of insects have appeared during centuries of use. Derris dust can also be used as an insecticide on crops.; The pounded roots are soaked in water to produce a fish poison, and the poisoned fish can be eaten without risk.; Selected clones of the crop are propagated vegetatively by cuttings of mature stems. But seed set is common and improvement by amateurs is feasible. However, there are no serious parasites of derris, and breeding for horizontal resistance appears to be unnecessary.; Derris is a short-day plant that needs a tropical forest ecology, and there appears to be no possibility of producing temperate cultivars.
Desert locust: See: Schistocerca gregaria.
Designated host: A genetically stable host (i.e., a clone or pure line) which has been chosen for use in the one-pathotype technique in a horizontal resistance breeding program.; The designated host has a resistance that is matched by the designated pathotype, which is cultured on that host for the entire duration of the breeding program.; All the original parents of the breeding population are chosen on the basis of their susceptibility to the designated pathotype, which is used to inoculate every screening population. This will ensure that all vertical resistances are matched during the screening for horizontal resistance, regardless of how the vertical resistance genes may have recombined during the crossing process.; Only one designated pathotype may be chosen for each species of parasite. The one-pathotype technique is necessary only when vertical resistances occur in the host species. However, its use is not always necessary, even then, and alternative techniques exist.
Designated pathotype: A pathotype (i.e., strain, or race) of a parasite which has been chosen for use in the one-pathotype technique in a horizontal resistance breeding program.; The designated pathotype is cultured on the designated host for the entire duration of the breeding program. All the original parents of the breeding population are chosen on the basis of their susceptibility to the designated pathotype, which is used to inoculate every screening population. This will ensure that all vertical resistances are matched during the screening for horizontal resistance, regardless of how the vertical resistance genes may have recombined during the breeding process.; Only one designated pathotype may be chosen for each species of parasite. The one pathotype technique is necessary only when vertical resistances occur in the host species. However, its use is not always necessary, even then, and alternative techniques exist.
Designation: See: Designated host; Designated pathotype.
Dessicator: A glass jar with a air-tight lid that is used for drying out small quantities of plant tissue, such as seeds or root nodules, with a dessicating chemical.; Dry calcium chloride is a powerful desiccating chemical, but it is toxic and must be kept well separated from living tissues. Alternatively, silica gel is harmless, but it is less powerful in its drying action.
Determinate habit: The converse of the climbing habit in plants, i.e. a bushy plant rather than a vine.; A determinate plant remains relatively small and close to the ground, like dwarf beans or potatoes. The determinate habit results from the terminal flower of an inflorescence opening first, and the stem grows no further.
Dew: See: Guttation.
Diallel cross: A polycross in which each parent is mated with every other parent.; In a full diallel cross, each parent is represented twice, once as a male and once as a female. More commonly, a half diallel cross is used, in which each parent is represented only once, either as a male or a female, but not both.; A half diallel cross is usually used at the start of recurrent mass selection. The alternative is to use a random polycross.
Dichotomous: A dichotomous stem is one that forks regularly into two branches.
Dicotyledon: Any Angiosperm that has two cotyledons. They are often called the broad-leaved plants.; Seeds of dicotyledons can be split into two halves (e.g., split peas) and they include all the peas and beans, most of the temperate fruits and nuts, crops of the cabbage, cucumber, and potato families, cotton, tobacco, rubber, tea, coffee, cocoa, cassava, sweet potato, and many vegetables, herbs and spices.
Dieback: A plant disease symptom in which stems die backwards from the tip. Diebacks are usually caused either by a pathogen attacking the young tissue of the stem tip, or by a disease in another part of the plant producing toxins that kill the growing point. They can also have a physiological cause, such as a nutrient deficiency.
Differential interaction: A table of host and parasite interactions (i.e., responses of resistances to parasitic abilities and vice versa) in which several different pathodemes are necessary to identify a pathotype, and several different pathotypes are necessary to identify one pathodeme.; A differential interaction is also known as a variable ranking, as opposed to the constant ranking that is typical of horizontal resistance and horizontal parasitic ability. The Person-Habgood differential interaction is the definitive interaction of vertical resistance and vertical parasitic ability.
Digitaria decumbens: A subtropical fodder grass native to Southeast Africa.
Dikaryon: A fungus in which each cell has two haploid nuclei, which are usually genetically distinct. Dikaryotic mycelium is thus equivalent to diploid mycelium. It occurs mainly in the rust fungi.
Dimorphous branching: Some crop species (e.g., arabica coffee, cotton, black pepper) have two kinds of branches. The orthotropic branch is the branch that grows vertically, and it produces side branches, called plagiotropic branches, that tend to grow horizontally.; It is usually the plagiotropic branches that bear the flowers and seed. cuttings must be taken from the orthotropic branch, and this severely limits vegetative propagation.
Dioecious: Greek = two houses (pronounced dye-ee-shous). A plant species in which the male and female sexes are separated in different plants. See also: Hermaphrodite.
Dioscorea alata: This is the Asian yam, also known as the white yam, the greater yam, the winged yam, and the water yam. See Dioscorea spp., for a description of the genus.; This yam was of major importance to the seafaring Polynesians who took it to most of the tropical islands of the Old World. It is propagated vegetatively, because most cultivars never produce fertile seed, and some are completely sterile.; Not recommended for amateur breeders. This is a crop with extinct wild progenitors.
Dioscorea bulbifera: This is the aerial yam, also known as the potato yam. It is of minor importance as a food crop but was probably important in ancient times. It is the only species that occurs wild in both Africa and Asia.; See Dioscorea spp., for a description of the genus. Not recommended for amateur breeders.
Dioscorea cayenensis: This is the yellow yam, also known as the twelve-month yam, and the yellow guinea yam. In spite of its name, this is a West African species that still occurs wild. It was taken to the New World with the slave trade.; It is widely grown in West Africa but it is not as important as Dioscorea rotundata. Not recommended for amateur breeders. See Dioscorea spp., for a description of the genus.
Dioscorea rotundata: This is the white yam, also known as the Guinea yam, and the eight-months yam. It originated in West Africa and is the most important species agriculturally.; Many clones exist but most of them set fertile seed so rarely that breeding is all but impossible. Not recommended for amateur breeders. See Dioscorea spp., for a description of the genus.
Dioscorea spp.: These are the true yams, not to be confused with sweet potatoes, which are called yams in the southern USA.; Although generally considered a monocotyledon, this genus has many features of dicotyledons, including reticulate veining in the leaves and occasional seeds with two cotyledons, in which only one cotyledon develops. The genus is very old geologically, and it occurs, and has been domesticated, in both the Old and the New Worlds. The principle species are described under their specific names.; The true yams are monoecious. Most cultivars are propagated vegetatively because they produce fertile seed rarely or not at all. This makes breeding extremely difficult, and these crops are not recommended for amateur breeders.; There are few pests and diseases of yams and, because all the cultivated clones are ancient, they are a useful demonstration of both the durability and the efficacy of horizontal resistance.; Wild yams were recently in danger of extinction due to the demand for natural diosgenin in the manufacture of oral contraceptives. However, the development of synthetic diosgenins has eliminated this threat.
Dioscorea trifida: The cush-cush yam is the only cultivated yam that is indigenous to the New World. Not recommended for amateur breeders. See Dioscorea spp., for a description of the genus.
Dioscorides: Pedanus Dioscorides was a first century Greek physician who wrote a standard work called De Materia Medica that concerned plants and minerals of medical significance.
Diploid: A cell or a plant with two sets of chromosomes. One set comes from each parent. Diploidy is the normal state in most plants and animals.; See also: Doubled monoploid, Haploid, Tetraploid, Triploid, Dikaryon.
Diptera: The Order of insects called flies, characterised by having only one pair of wings. This is one of the largest orders of insects.; The Order includes biting insects such as black flies, mosquitoes, and sand flies. Houseflies are carriers of human diseases such as typhoid and cholera, and this was the first insect to develop resistance to DDT.
Dirty Dozen: The list of the twelve most persistent organic pollutants (POPs) banned at a United Nations convention in May 2001. Nine of the chemicals in this list are crop protection chemicals and, of these, eight are insecticides.
Discontinuity: See: Discontinuous pathosystem.
Discontinuous epidemic: See: Discontinuous pathosystem.
Discontinuous pathosystem: A pathosystem in which the parasitism is intermittent because there is a complete absence of host tissue at periodic intervals, such as during a tropical dry season, or a temperate winter.; Discontinuous pathosystems involve seasonal host tissue, and they occur typically with annual plants, and the leaf parasites of deciduous trees and shrubs.; Discontinuity confronts the parasite with three difficult problems, because it must survive the absence of host tissue, it must find a new host individual when tissue is again available and, if vertical resistance occurs, it must match the host that it does find.; Allo infection is of primary importance in discontinuous pathosystems, and vertical resistance has a high survival value.; Note that discontinuity and vertical resistances can occur in the parasitism of the winter hosts of heteroecious rusts and aphids even though these hosts may be perennials. This is because the parasite is oblidged to migrate to its summer host.; See also: Continuous pathosystem.
Discontinuous variation: In genetic terms, variation among individuals may be continuous or discontinuous. Continuous variation means that there is every degree of difference between two extremes. Discontinuous variation means that a character is either present or absent, and there are no intermediates.; Continuous variation results from quantitative inheritance, while discontinuous variation results from qualitative inheritance.
Disease: Plant diseases usually have the most colourful names, such as blight, downy mildew, powdery mildew, blast, rust, smut, smudge, wart, streak, blister, and scorch.; Plant diseases are caused by parasitic organisms called pathogens, that are usually microscopic, and which include fungi, bacteria, phytoplasmas, viruses, and viroids.; The development of a disease within a host population is called an epidemic.; Deficiency diseases are due to nutritional inadequacies and are best described as physiological disorders.
Disease cycle: See: Epidemic cycle.
Disease escape: For a variety of reasons, some individuals in a screening population may remain free of pests or disease. Also known as chance escape, this phenomenon can be very misleading because it is so easily confused with resistance.; See also: inoculation, patchy distribution.
Disinfection: In a plant protection context, this term means destroying the initial inoculum in order to control the epidemic. Disinfection is undertaken most commonly with contaminated seed and infected seed. But it can also refer to storage containers, with a view to reducing post-harvest losses.
Disinfestation: This term means the same as disinfection except that it normally refers to insects.
Dissecting microscope: A low power, stereoscopic microscope with two optical systems that provide a three-dimensional view.
Dissemination: The geographical spread of pests or disease.; The natural dissemination of fungi is usually by wind-borne spores, while insects usually travel by flight, often assisted by wind. However, dissemination can also occur with irrigation water, contaminated or infected seed, muddy boots or tractor wheels, international trade, travellers, etc.
Distal: That part of a plant organ that is most distant from its point of attachment. See also: Proximal.
Distribution, normal: See: Normal distribution.
Dithiocarbamates: A group of synthetic fungicides developed during the 1920s and 1940s that are popular mainly because they are stable.
Diurnal: During daylight hours, as opposed to nocturnal.
Diversity: See: genetic diversity.
Dizygotic: Dizygotic twins develop as two separate embryos produced by two separate ova fertilised by two separate sperm. Also known as fraternal twins.; See also: Monozygotic.
DNA: Di-ribo-nucleic acid. The protein which encodes genetic information, and controls all things inherited. In plants and animals, the DNA is located in the chromosomes.
Dodder: See: Cuscuta spp.
Dolichos lablab: See: Lablab niger.
Domestication: The process by which ancient cultivators changed wild plants into crop plants by artificial selection.; Usually, domestication was a very gradual process in which cultivators tended to use their best plants as parents for the next crop, producing quantitative improvements. Occasionally, however, domestication would progress in sudden and dramatic developments, with qualitative changes, as when both the non-shattering and free-threshing forms of wheat were discovered.; These changes occurred thousands of years ago, and the descendants of those forms have been in continuous cultivation ever since. Ancient domesticators often achieved results that modern plant breeding cannot improve as, for example, with pineapples, bananas, olives, and the classic wine grapes.; A few plant species were domesticated quite recently. These include rubber (Hevea brasiliensis) and oil palm (Elaeis guineensis).
Dominant character: A genetic character is described as dominant when its controlling allele eclipses the recessive allele.
Dormancy: Inactive, as in sleep. Many seeds exhibit dormancy, which is a valuable ecological and evolutionary survival mechanism that ensures survival of the species in the event of some disaster that destroys all non-dormant individuals.; Dormancy can be a nuisance in agriculture, and in plant breeding. It can often be broken by mechanical or chemical reduction of the seed coat, or by temperature treatment of the seed.
Dottato: An ancient Roman cultivar of fig that was mentioned by Pliny the Elder (23-79 AD) and which is still being cultivated in Italy. This is an example of an ancient clone demonstrating the durability and efficacy of horizontal resistance.
Doubled monoploid: A monoploid (i.e., haploid) cell or plant that has undergone a doubling of its chromosomes to produce a functional diploid.; Doubled monoploids are produced artificially, usually by culturing a pollen mother cell, or a pollen cell, into a haploid plantlet, which is then stimulated chemically to double its chromosome number. Alternatively, an unfertilised ovule can sometimes be made to grow into a haploid plantlet by pollination with pollen from a different species.; Doubled monoploids are completely homozygous, and this can be very useful in various plant breeding procedures.; See also: Haploid, diploid, Tetraploid, Triploid.
Douglas fir: See: Pseudostuga menziesii.
Downy mildews: Plant parasitic fungi of the Order Peronosporales, so called because they produce a very light, white mildew on the external surfaces of the plant lesions, usually on the lower leaf surfaces.; The best known members are potato blight (Phytophthora infestans) and downy mildew of grapes (Plasmopora viticola). Downy mildews were originally controlled by Bordeaux mixture.
Dried blood: Obtained from slaughter houses, dried blood is often used as an organic fertiliser. However, the supply is limited.
Drought resistance: The ability of a plant to withstand drought. This property can be very valuable in areas of uncertain rainfall. For example, sorghum has greater drought resistance than maize, and is grown in many semi-arid areas for this reason.
Duram wheat: See: Triticum durum.
Durra: See: Sorghum bicolor.
Dwarf varieties: See: Wheat, and Rice.
Dysmicoccus brevipes: The mealy-bug that causes wilt of pineapples. There is great need for horizontal resistance to this pest but this is not a task for amateur breeders.

Glossary: E

Early selection: Selection during an early generation after cross pollination when the selected individuals are heterozygous.; Early selection is usually acceptable in allogamous species but not in autogamous species.; Its advantage is a considerable shortening of the breeding cycle. Its disadvantage is that heterosis may give a false impression of resistance and yield, and that recessive polygenes will remain unexpressed.; These disadvantages are eliminated with late selection.
Echinochloa frumentacea: Japanese barnyard millet. This millet is the fastest growing of any cereal, and can produce a harvest in little more than forty days. It is grown as a minor cereal in the Orient and India, and as a fodder crop in North America where it can produce up to eight crops a year. A fun project for amateur breeders.
Ecology: The study of the interactions of species, or populations, with each other, and with their environment. Ecology makes considerable use of systems theory, and the concept of the ecosystem. It also tends to emphasise the higher systems levels, and the holistic approach.; See also: Pathosystem.
Economics, agricultural: One of the disciplines that make up crop science. Like general economics, agricultural economics can be divided into macro- and micro-economics.; See also: Self-organising crop improvement.
Ecosystem: A biological system that occupies a specified area, and which involves the interactions of all the living organisms in that area, both with each other, and with their environment.; A subsystem of the biosphere, defined by either geographical or biological boundaries.
Ecotype: A local variant that has been produced by selection pressures peculiar to its own locality within the ecosystem. Ecotypes are the result of micro-evolution and natural selection.; See also: cultivar, Landrace, agro-ecotype.
Edaphic: Pertaining to soils.
Eddoe: See: Colocasia esculenta.
Eelworm: The colloquial term for a nematode, or round worm.
Eggplant: See: Solanum melongena.
Elaeis guineensis: The oil palm, which is native to West Africa.; This palm has the highest yield of vegetable oil of any crop. The oil is obtained from the fruit which contains two distinct types of oil. Palm oil is extracted from the soft fruit flesh, which contains 45-55% of oil. Palm kernel oil comes from the seed, which contains about 50% of oil.; This is not a crop for amateur breeders.
Electron microscope: A microscope that uses electrons instead of light. It has the advantage of a far higher resolution that can show virus particles. But it is a very technical and expensive instrument.
Elephant garlic: See: Allium ampeloprasum.
Elephant grass: See: Pennisetum purpureum.
Elletaria cardomomum: Cardamom. This genus is native to S.E. Asia and is a member of the ginger family, Zingiberaceae. The fruits are widely used as a spice, and are particularly prized in Arab countries for adding to coffee.; The plants are open-pollinated and offer scope for amateur breeders located in areas suitable for cultivation.
Elusine coracana: Finger millet, also known as African millet, as well as wimbi, bullo, telebun, and other vernacular names.; It is an important crop in the drier areas of Africa and India, although sorghum and bulrush millet are more drought-resistant. It has a wide range of uses as flour, as an additive to various dishes, and for brewing. In a dry climate, it stores well for up to ten years.; Finger millet is self-pollinated and there are innumerable cultivars in both Africa and India. A suitable crop for amateur breeders, who should start by selecting within local landraces that are mixtures of inbreeding lines.
Emasculation: The physical removal of the anthers from a hermaphrodite flower, or the male flowers from a monoecious plant, in order to prevent self-pollination, and to compel cross pollination.; Alternative methods involve the use of a male-sterility gene, or a male gametocide.
Embryo: An unborn, unhatched, or ungerminated offspring. An embryo normally results from the fusion of a male gamete with a female gamete. However, in plants, nucellar embryos and apomictic seeds are also possible.; See also: Metaxenia.
Emergent property: This concept was first defined by C.D. Broad some eighty years ago. An emergent property is one that emerges at a particular level of complexity, a particular systems level, but which cannot occur at a lower systems level. Thus, the system of locking of the gene-for-gene relationship is an emergent that is possible only at the systems level of the two interacting populations of the pathosystem.; There must be a population of many different locks, and many different keys, if a system of locking is to function. At the lower systems levels of an individual lock, or an individual tumbler within a lock, a system of locking is impossible. The danger of doing research at too low a systems level is that an emergent may not be apparent. This is a major cause of suboptimisation.; Possibly the best example of emergent properties in biology is the schooling of fish, and the flocking of birds. A scientist studying a single fish in an aquarium, or a single bird in an aviary, cannot possibly observe the phenomenon of schooling or flocking because this property emerges only at the systems level of the population.
Empirical science: Science that emphasises facts, as opposed to concepts and theories. Its converse is rationalism. Either extreme constitutes bad science, and good science must be a blend of both facts and theories.
Endemic: 1. An endemic species is one that is uniquely present in a locality.; 2. An endemic disease is one that is continuously present, as opposed to an epidemic disease, which is intermittently present.
Endive: See: Cichorium.
Endosperm: The nutritive material, usually oil or starch, stored in some seeds.
Endothia parasitica: The fungus that was accidentally introduced to America from Europe early in the twentieth century. It causes ‘chestnut blight’ and it destroyed the wild chestnut forests of North America.
Engineering, agricultural: One of the many disciplines that makes up crop science. It is concerned primarily with agricultural machinery.
Ensete: See: Ensete ventricosa.
Ensete ventricosa: This member of the banana family is grown for food in Ethiopia. Ensete edule is also cultivated for food in this area. These crops are not recommended for amateur breeders.
Entomologists: Scientists who study the science of insects, or entomology.
Entomology: The scientific discipline concerned with the study of insects. Crop entomology is concerned with the study and control of insects that are crop parasites, crop pollinators, or agents of biological control and integrated pest management.
Entropy: The degree of disorder or randomness of the constituents of a system. In a closed system, entropy increases. That is, all energy gradients disappear, and complexity of pattern is reduced to total simplicity of pattern.; Its converse is negative entropy (negentropy). In an open system, negentropy can increase. All living systems are open systems.
Environment: Approximately synonymous with habitat, the environment can be defined as all the external conditions that affect the survival and growth of an organism.
Enzyme: An organic catalyst, which can both promote and control a specific biochemical reaction.
Ephemeral: Short-lived, temporary.
Epidemic: Parasitism at the systems level of the population.; An epidemic may be continuous or discontinuous, and this determines the relative importance of the two kinds of resistance, and the two kinds of infection. A continuous epidemic is sometimes called an endemic but this usage is best avoided.; See also: Epiphytotic, Epizootic.
Epidemic cycle: An epidemic cycle occurs with a discontinuous epidemic, and it concerns the overall development of an individual epidemic, from the initial inoculum of the parasite to its population extinction.; An epidemic cycle normally coincides with a growing season, such as a summer in temperate regions, or a rainy season in the tropics. However, the epidemic cycle of rubber in the Amazon Valley is defined by the deciduous nature of the rubber tree, whose leaf-fall is independent of season in this continuously warm and wet environment.
Epidemiological competence: A parasite can cause an epidemic only if it has epidemiological competence in the area in question. The level of epidemiological competence can vary from one area to another, and from one season to another, and it is controlled mainly by climatic factors such as temperature and humidity.; For example, the maize disease called ‘tropical rust’ (Puccinia polysora) lacks epidemiological competence outside the lowland tropics. Maize cultivars in Europe are highly susceptible to this disease, but they are not vulnerable to it, because of its inability to cause an epidemic in a temperate climate. The susceptibility of these European maize cultivars becomes apparent only if they are cultivated in the lowland tropics.; Variation in epidemiological competence explains the need for on-site selection when breeding for horizontal resistance.
Epidemiology: The study of epidemics, which requires both a holistic and a mathematical approach.
Epidermis: The outermost tissue of leaves and herbaceous stems. The epidermis usually consists of a single layer of cells, often protected by a layer of wax.; The pattern of cells, similar to that of a jigsaw puzzle, is often characteristic of a particular species, and can be used during research for plant identification in animal feces, and in certain forensic situations.; Stomata are a component of the epidermis.
Epiphyte: A plant that lives on another plant without being parasitic. For example, moss and lichen growing on a branch of a tree are epiphytes.
Epiphytotic: A somewhat pedantic term, sometimes used to describe an epidemic in plants, on the grounds that the Greek root demos refers to people. But the term ‘epidemic’ is an English word, and common usage allows it to be applied to plants and animals.; Note that epiphytology is the study of epiphytes, and that the study of epiphytotics is epiphytotiology. These usages are not recommended. See Also: Epizootic.
Epizootic: A somewhat pedantic term (pronounced epi-zoh-otic), sometimes used to describe an epidemic in animals. The study of epizootics is epizootilogy. These usages are not recommended. See also: Epiphytotic.
Eradication: Eradication, like the word ‘unique’, is a word that should be used with caution. Eradication is an absolute, which either does or does not succeed. In the present context, it means the total and complete elimination of a pest or disease, within a stated area.; For example, eradication of the accidental introduction of Colorado beetle of potatoes in Germany was successful, but attempts to eradicate a later introduction in France failed, and this pest then became firmly established in Europe. Occasional appearances of the beetle in Britain have been successfully eradicated.
Eragrostis curvula: A subtropical fodder grass native to Southeast Africa.
Eragrostis tef: This cereal is unique to Ethiopia where it is used for the production of the staple dish ‘njera’. It is also an excellent fodder crop. The self-pollinated flowers are very small and this makes cross pollination extremely difficult. Not recommended for amateur breeders.
Ergotism: The human disease caused by the ingestion of poisonous ergots. The symptoms of ergotism are a constricting of the blood vessels which can lead to gangrene, abortion in pregnant women, and death.; Before the discovery of the cause of this disease, ergots were common in rye produced in a wet summer, and ergotism was a powerful incentive for the cultivation of potatoes in the rye districts of Europe, particularly in eastern Germany, Poland, and western Russia.; Today, ergots are recognised and easily separated from rye before milling. They have a market value in the pharmaceutical industry as an aid to childbirth.
Ergots: Toxic black bodies produced in rye by the fungus Claviceps purpurea. Toxic ergots are also produced by Claviceps penniseti in bulrush millet. When ingested, ergots are the cause of the human disease ergotism.
Erosion of horizontal resistance: A quantitative loss of horizontal resistance. There are four categories of erosion:; 1. A host erosion results from genetic changes in the host. This can occur during the cultivation of a genetically flexible crop, but not during the cultivation of a genetically inflexible crop. It can also occur during the breeding of any crop in the absence of a parasite, particularly if the screening population is protected by a functioning vertical resistance or by a pesticide. It is then known as the vertifolia effect.; 2. An environment erosion results when a cultivar is taken from an area of low epidemiological competence, and is cultivated in an area of high epidemiological competence.; 3. A parasite erosion results from genetic changes in the parasite. This is important only occasionally, and only with facultative parasites.; 4. A false erosion results from sloppy experimental work, when a cultivar thought to be resistant is later found to be susceptible.
Erysiphales: The plant-pathogenic powdery mildews, characterised by growing on the external surfaces of plants.; This Order contains six genera defined by the cleistothecia, which may have one or several asci, and various types of appendage: Erysiphe (several asci, simple appendages), Sphaerotheca (one ascus, simple appendages), Microsphaera (several asci, dichotomous appendages), Podosphaera (one ascus, dichotomous appendages), Phyllactinia (several asci, rigid appendages), and Uncinula (several asci and curled appendages).; The imperfect stage, consisting of hyphae and conidia only, is called Oidium.
Erysiphe: A genus of the Erysiphales, or powdery mildews.; The most important species are Erysiphe graminis, which attacks wheat, barley, rye, oats, and many fodder grasses; Erysiphe polygoni, which attacks peas, clovers, and swedes; and Erysiphe cichoracearum, which has a wide host range that includes various cucurbits, tobacco, and many ornamentals.; Vertical resistances are common and there is considerable scope for breeding for horizontal resistance by amateurs.
Erythroxylon coca: Coca, the source of cocaine, native to tropical and subtropical South America.
Escapes from parasitism: See: Chance escape.
Essential oils: This term means ‘essence’ rather than indispensable. Essential oils are obtained from a wide variety of plants, and the oil is extracted either by distillation or by solvents, which are then evaporated off and reused.; Most essential oils are used in the perfume industry and for aromatherapy, but a few also have medicinal uses. Many of them offer scope for amateur breeders who, however, should be aware of the limited markets that are easily saturated.
Ethrel: The trade name for ethephon, which is 2-(chloro-ethyl)-phosphonic acid. It is an ethylene (ethene) generator when applied to plant surfaces. Ethylene has numerous physiological effects, such as inducing synchronous flowering and fruit ripening, which assists mechanical harvesting, etc.; Ethrel is also used as male gametocide to induce random cross pollination for recurrent mass selection in inbreeding cereals such as wheat.
Eucalyptus spp.: A genus of trees, known as gum trees, originating in Australia. These fast-growing trees are an excellent source of firewood in areas that are short of fuel for cooking. They are now widespread throughout the tropics and subtropics. There is considerable scope for amateur breeders to select within existing populations for fast growth.
Eucaryote: All organisms, other than bacteria and cyano-bacteria, are eucaryotes, and they are characterised by consisting of cells that contain a distinct nucleus enclosed in a membrane and containing chromosomes, as well as other specialised organelles.; See also: Procaryote.
Eugenia carophyllus: The clove tree, which originated in the spice islands of the Moluccas, in eastern Indonesia.; The cloves of commerce are the dried, unopened buds, and they became a monopoly of the Portuguese in the early sixteenth century. The Dutch gained the monopoly in 1605, and kept it for two centuries. Later, cloves were taken to many areas, but they flourished best in Zanzibar, which became the main producer.; Cloves are now grown increasingly in Indonesia, where they are in great demand for clove cigarettes.
Evergreen: Evergreen trees and shrubs have persistent leaves and continuous pathosystems and, consequently, a gene-for-gene relationship and vertical resistance will not evolve in them. A gene-for-gene relationship can evolve only in a discontinuous pathosystem. See also: Deciduous.
Evolution: The results of natural selection, often described as the survival of the fittest.; Macro-evolution (or Darwinian evolution) occurs during periods of geological time, and involves genetic changes that are both new, and irreversible. New species are formed by macro-evolution. Macro-evolution also produces an increase in complexity, and new genetic code.; Micro-evolution occurs during periods of historical time, and it involves genetic changes that are not new, and that are reversible. It does not increase complexity, but merely reorganises existing complexity. Nor does it produce new genetic code; it merely rearranges existing code.; The formation of ecotypes is micro-evolution by natural selection, and the production of cultivar or agro-ecotypes, by plant breeding is micro-evolution by artificial selection.; The mechanism of evolution has long been disputed and is now thought to be the result of natural selection operating on emergents at all systems levels.
Examples of horizontal resistance: See: horizontal resistance, examples.
Exobasidium vexans: The fungus that causes blister blight of tea. There is great scope for selection for horizontal resistance within existing crops grown from true seed, as these crops constitute a vast hybrid swarm.
Exoskeleton: The hard external surface of all arthropods, including the insects. Because the exoskeleton cannot expand or grow, it must be shed or moulted at several stages during the growth of the individual arthropod. See also: Instar.
Extension service: The service that provides technical and specialised information to farmers. In the USA, the extension officers are known as county agents. It is rare that they are trained in alternative techniques like organic farming and horizontal resistance breeding.
Extensive crop: A crop that has low production costs and profit margins. Soybeans, maize, and wheat are typical extensive crops in North America.; See also: intensive crop.
Extinct wild progenitors: Crops whose wild progenitors have been harvested by ancient hunter-gatherers to extinction.; The domesticated forms survived because farmers are always careful to preserve propagating material of their crops. But food gatherers may be careless about wild plants and, in the course of a few human generations, they may not have noticed the decline in numbers that was occurring because of their activities.; Among ancient clones, this loss of wild progenitors has occurred with black pepper, garlic, ginger, olive, saffron, and turmeric.; Among other crops, a loss of wild progenitors also occurred with broad bean, cassava, chillies, green peas, onions, peanuts, soybean, sweet potato, tea, turmeric and yams.
Extinction: The total loss of a species resulting from either natural competition, or the activities of humankind.

Glossary: F

f.sp.: See: forma specialis
F₁, F₂, etc.: The letter ‘F’ stands for ‘filial’ and refers to the generation. Thus F₁ is the first generation (sons), F2 is the second generation (grandsons), and so on, following the cross of two parents, that are labelled P.; This nomenclature is used mainly with autogamous crops and refers to the self-pollinating generations that follow cross pollination.
Facultative parasite: A parasite that is able to extract nutrients from both a living plant host, and from dead plant material. See also: Obligate parasite.
Fagopyrum spp.: Buckwheat. This one of the pseudo-cereals.; Three species are cultivated. Fagopyrum esculentum is the common buckwheat, F. cymosum is the perennial buckwheat, and F. tataricum is the Tartary buckwheat.; The buckwheats are a very ancient crop originating in China. They are not very important commercially but they have persisted agriculturally for many millennia.; They are open-pollinated and amenable to general improvement by amateur breeders using recurrent mass selection. There is room for improvement in horizontal resistance to both pests and disease.
Fagus sylvatica: The beech. A hardwood tree used in plantation forests. Not recommended for amateur breeders.
Family: A taxonomic group of closely related genera.
Family selection: When working with pure line crops, the technique of family selection, or ‘head to row’ selection, can lead to a more rapid genetic advance.; Family selection means that all the seeds derived from one ‘head’ or ‘ear’, or from one plant, constitute a ‘family’. All the members of one family are planted together, in one row, or in one small plot.; The selection is in two stages. The first stage selects the best families. The second stage selects the best individual plants within those best families. Only the best individuals, from the best families, are kept.; Note: This term has nothing to do with the taxonomic group called a family.
FAO: See: Food & Agriculture Organisation of the United Nations.
Farm animal breeding: The breeding of farm animals deserves a mention in a guide to plant breeding for one simple reason. There are no single-gene characteristics of any economic significance in farm animals.; The domination by Mendelian breeders that occurred in professional plant breeding, has been avoided in animal breeding. The improvement of farm animals has involved population breeding, often conducted by individual farmers.; However, a feature common to both kinds of breeding is that heterosis has been exploited in poultry breeding. More recently, artificial insemination has caused a considerable loss of genetic diversity in some species.
Farmer participation schemes: The process of ‘farmer participation’ in plant breeding is to allow farmers some influence in the production of new cultivars.; The participation can vary from the one extreme of a farmer-survey to determine farmer preferences, to the other extreme of the farmers doing the actual breeding -- which we welcome you to do in association with OPBF -- and possibly under the guidance of a professional breeder.
Farmer selection: This is an aspect of some plant breeding programs, including ours, in which the farmers make the final selection of cultivar. It is also known as participatory plant breeding.; Each farmer is given a different group of new clones or pure lines of a crop, emerging from a breeding program. They then grow them and choose those they like best. Their favourites become their own property, with the sole provision that the breeder may have some of them for the purpose of further breeding. The farmers may then grow that material for their own use, and give or sell propagating material to their friends and neighbours.; This farmer selection represents one of the first steps in self-organising crop improvement.
Farmer’s privilege: This is a clause in the plant breeders’ rights legislation of most countries that permits a farmer to use some of their own crop of a registered cultivar for seed on their own farm only. A farmer may not sell any of that crop for seed unless licensed to do so.; However, some seed companies deny this right, particularly with respect to GMOs, by a special clause in the sale contract.; See also: Breeders’ rights.
Farmyard manure (FYM): The composted excrement of farm animals, mostly cattle, pigs, and horses, but also poultry, and usually mixed with straw, used as a fertiliser for crops. Organic farmers use only natural (i.e., non-synthetic) fertilisers and FYM is one of the most important of these.
Feed grains: Grains, mostly cereals, used for feeding farm animals. Maize is the most important of the feed grains.
Feedback: The modification or control of a process or system by its own results.; Feedback can be either positive or negative. Positive feedback leads to increase and is destabilising. For example, population growth depends on the number of reproducing individuals. As the population increases, the rate of growth also increases, and there can be a population explosion.; Negative feedback leads to stability. For example, an excess of individuals limits the available food, and leads to a loss of breeding individuals. The population size is then stable.; See also: Homeostasis.
Female sterility: Some crops (e.g., banana) do not produce true seed because of a female sterility. However, male sterility is much more common, and is more useful in plant breeding as a technique for achieving cross-pollination.
Fermentation: Fermentation is the alteration of biological substances by either microbiological or chemical means.; Microbiological fermentation may be constructive (e.g., the production of penicillin) or destructive (e.g., the breakdown of sugars into carbon dioxide and alcohol, in beer, wine, and bread).; Chemical fermentation occurs without the participation of micro-organisms and it occurs, for example, in the fermentation of green tea into black tea, and in the production of silage.
Fertile Crescent: An archaeological term used to describe the fertile area of ancient agriculture that extends from modern Israel in a wide arc to the valley of the Tigris and Euphrates rivers.
Fertilisation: This term, which is derived from ‘fertile’, has two meanings in crop science. It can refer to the feeding of crops with compost, farmyard manure or artificial fertilisers; and it can also refer to the sexual fertilisation of a female ovule by a male pollen cell.
Festuca arundinacea: Fescue is a grass used widely for sown pastures. There are technical problems in its breeding.
Feterita: See: Sorghum bicolor.
Fibre: Plant fibres give strength to stems.; Some of them can be retted to provide bast fibres for the manufacture of coarse materials such as sacking, sails, and tarpaulins. The most important of these are flax (Linum usitatissimum), hemp (Cannabis sativa), Manila hemp, or abaca (Musa textilis), Sunn hemp (Crotalaria juncea), jute (Corchorus spp.), and sisal (Agave sisalana).; With the development of plastic fibres, the demand for natural bast fibres has decreased dramatically. These crops are now relatively unimportant. Flax, hemp, and sunn hemp are easy to breed, but Manila hemp and sisal are not recommended for amateur breeders.; Note that cotton is a plant fibre, but it is not a bast fibre and it remains a very important crop. There is also some development in the use of hemp and bamboo fibres in fabrics and clothing.
Ficus carica: The edible fig. This is a vegetatively propagated crop of very ancient domestication, which originated in southern Arabia. It has been cultivated in the Mediterranean basin since antiquity and, more recently, it has been taken to all suitable areas of the world.; Several Mediterranean countries produce large amounts of dried figs, and fig paste, for export. The so-called fruit is a complex organ containing numerous minute flowers on its inner surface, and these are pollinated by the fig wasp (Blastofaga psenes), which enters through a very small pore at the distal end.; About 600 distinct clones have been recognised. Dottato is an ancient Roman cultivar of fig that was mentioned by Pliny the Elder (23-79 AD) and which is still being cultivated in Italy. These figs are of interest because of their ancient clones, which demonstrate both the utility and the durability of horizontal resistance.; Fig breeding is technically complicated, and is not recommended for amateur breeders.
Field resistance: Resistance that is apparent in the field but not in the laboratory. This vague term has been widely misused and is best avoided. It is sometimes used, incorrectly, as a synonym for horizontal resistance. See also: Tolerance.
Field screening: A screening operation that is conducted in the field, as opposed to the greenhouse, or the laboratory. Because of the necessity for on-site selection, amateur breeders working with horizontal resistance should always employ field screening, except for a final laboratory screening for certain aspects of quality, which cannot be determined in the field.
Field trials: Typically, these are statistical trials carried out under field conditions. The statistics involved used to be the bane of agricultural students’ lives but these days they are handled entirely by computer.; Note that statistical trials are very valuable when comparing cultivars, spacing, or fertiliser use for variables such as yield and crop quality. But they can be very misleading when comparing treatments for the control of crop pests and diseases, because of parasite interference.; Note also that statistical trials measure the probability of small differences being real differences. Big increases in yield or horizontal resistance do not need statistical trials and, for this reason, they are not usually necessary for amateur breeders.
Fig: See: Ficus carica.
Filbert: See: Corylus avellana.
Finger millet: See: Eleusine coracana.
Fir, Douglas: See: Pseudostuga menziesii.
Fire-blight: A disease of trees in the Rosaceae family (e.g., apple, pear, hawthorn) caused by a bacterium called Erwinia amylovora. Diseased trees appear to have been scorched by fire.
Flatulence: Most grain legumes cause flatulence because they contain proteins that are indigestible, and which ferment in the lower bowel to produce carbon dioxide and other gasses. Some reduction of the flatulence factors is possible by breeding, and this could be a breeding objective of amateur breeders.
Flax: See: Linum usitatissimum.
Flecks, hypersensitive: See: Hypersensitive.
Flexibility: See: Genetic flexibility.
Flocking of birds: The phenomenon in which birds in flight behave as a single entity. This behaviour is thought to provide protection against predators. It is an excellent example of an emergent property that is observable only at the systems level of the population.; A scientist studying a single bird (e.g., a pigeon) in an aviary could not observe or analyse the flocking habit. This failure to work at the higher systems levels constitutes suboptimisation. See also: Schooling, n/2 model.
Floret: A single flower in an inflorescence that is made up of many flowers grouped together.
Flower: The reproductive structure of seed-bearing plants, containing either specialized male or female organs (dioecious, monoecious), or both male and female organs (hermaphrodite), such as stamens and a pistil, enclosed in an outer envelope of petals and sepals.
Fodder beet: See: Beta vulgaris.
Fodder crop: Any crop that is grown for feeding farm animals, such as hay, turnips, mangolds, fodder beet, fodder legumes, and fodder grasses.
Fodder grasses: Members of the botanical family Gramineae cultivated for feeding farm animals, as hay, silage, or pasture. See also: Tropical grasses, Pasture grasses.
Fodder legumes: Members of the botanical family Leguminoseae cultivated for feeding farm animals. This tem includes alfalfa, clovers, and vetches, but the pulses are not generally used as fodder.
Foliage: See: Leaf.
Fomes spp.: Basidiomycete bracket fungi that attack various species of forest trees, including rubber in the Amazon Valley. The brackets grow out of the base of the tree and have spore-bearing tissues in the form of pores (as opposed to gills) on the lower surface.
Food & Agriculture Organisation of the United Nations (FAO): FAO has its headquarters in Rome, Italy, and was one of the first agricultural institutions to promote the use of horizontal resistance in its International Program for Horizontal Resistance (FAO/IPHR).
Food chain: The food chain is an ecological concept, and it is a form of eating hierarchy, with the smallest and most numerous animals at the bottom of the hierarchy. These animals may eat plants or each other. With increasing rank, the numbers get smaller, and the animals get larger.; As a general rule, the animals of one rank eat animals in a lower rank (except for parasite which may inhabit animals much larger than themselves). Each rank may be thought of as a link in a chain that stretches from the lowest to the highest level. Animals in any rank may also eat plants.; A low concentration of toxins, particularly fat-soluble and water-insoluble toxins such as DDT, in the environment tends to increase as it travels up the ranks of the food chain (see biomagnification), and it may reach dangerous levels at the top of the chain, in birds of prey, and large mammals, including people.
Foreign parasites: Species of plant parasites that are absent from an area, but which could become serious if accidentally introduced. Foreign parasites are the main cause of crop vulnerability.
Forestry: The cultivation of trees for timber. This term also includes the exploitation of natural forests for timber. Many forest tree species offer scope for amateur breeders, mainly by selection within existing populations. However, because most forest species are open-pollinated, a good parent tree will be only a half-sib.
forma specialis: Usually abbreviated to ‘f.sp.’ (singular) and ‘f.spp.’ (= formae speciales, plural) this taxonomic term means ‘special form’ and is a subdivision of a species of a parasitic fungus that is defined by its host.; Thus Fusarium oxysporum has various formae speciales defined by hosts as widely different as banana, flax, tomato, and date palm. A forma specialis can parasitise only its own host genus, and there are usually wide differences in the levels of horizontal resistance within that genus.
Foundation stock: The original source of seed from which all other grades of seed are produced.
Four-angled bean: See: Psophocarpus tetragonobolus
Foxtail millet: See: Setaria italica.
Fragaria ananassa: The cultivated strawberry, which is one of the most popular and widely cultivated of the soft fruits.; It is an open-pollinated, dioecious, octoploid (2n = 8x = 56) and is a member of the botanical family Rosaceae. Each cultivar is a clone that is propagated vegetatively by runners.; The species exhibits very wide variation and there is scope for amateur breeders. The main breeding objectives, other than yield and fruit quality, are horizontal resistance to various pests and diseases. Suitability for mechanical harvesting also has a high priority, and amateur breeders should know something of the machines available.
Frankincense: Known as olibanum in its centre of production in eastern Africa, frankincense (Old French franc encens = pure incense) is an aromatic gum obtained from trees of the genus Bowellia and, when thrown on to glowing charcoal, it produces an aromatic smoke. Little scope for amateur breeders.
Free enterprise in plant breeding: For most of the twentieth century, plant breeding was considered an esoteric subject that could be handled only by highly trained geneticists. This was largely because of the many difficulties encountered by pedigree breeding for single-gene, vertical resistance.; With the very different approach to breeding for horizontal resistance, using population breeding and recurrent mass selection, plant breeding is so easy that it can be undertaken by amateurs, particularly with the assistance of OPBF or another plant breeders association. When there are many such breeders in the world, there will be widespread free enterprise in plant breeding.
Free trade: Free trade was the key to Adam Smith’s (1723-90) economic theories, which he published in The Wealth of Nations in 1776. His ideas were closely similar to those of modern complexity theory, which recognises the importance of self-organisation in a non-linear system.
Frequency of parasitism: The frequency of parasitism is the proportion of host individuals that are parasitised. The injury from parasitism is the actual amount of damage done to an individual host, or the average amount done to a host population, by the parasite.; In a wild plant pathosystem, the injury from parasitism is inversely proportional to the frequency of parasitism. That is, the higher the frequency, the lower the injury, and, conversely, the higher the injury, the lower the frequency. In this way, the total damage from parasitism never exceeds a tolerable level that does not impair the host's ability to compete ecologically and evolutionarily.; Vertical resistance, with its system of locking, reduces the frequency of parasitism. Horizontal resistance, as a second line of defence, reduces the injury from parasitism. Continuous plant pathosystems, that have horizontal resistance only, usually have a high frequency of parasitism, and a low injury from parasitism.
Frost: Frost damage to frost-sensitive plants can easily be mistaken for an infectious disease. See: Physiologic disorder.
Fruit: In its wide botanical sense, a fruit is any ripened ovary, or group of ovaries, and the associated tissues. More generally, the term is restricted to those fruits, which offer a reward, in the form of sweetness and food, to animals that eat the fruit and unconsciously spread the seed, often in feces, which are deposited far from the parent plant.; The production of true seed in fruit, often as a result of cross-pollination, is an essential aspect of plant breeding. In a culinary context, savoury fruits (e.g., tomato, cucumber, peppers, egg plant) are called vegetables, and sweet vegetables (e.g. rhubarb) are called fruits.
Fu-fu: A traditional West African dish originally made from yams (Dioscorea) but more recently from Xanthosoma sagittifoilium.
Fuggle hops: See: Humulus lupulus.
Fumigation: Fumigation is aimed at killing pests with a gas or smoke. The most frequent use is in greenhouses and warehouses. A specialised use is in the treatment of imported produce to keep out foreign pests.; One of the most effective fumigants was methyl chloride, but this substance is now banned because of the damage it does to the ozone layer.
Fungi: Originally classified as non-flowering plants that lacked chlorophyll, fungi are now put in a separate kingdom.; Most fungi are microscopic and haploid, producing a shortlived diploid form only as a result of sexual fusion.; The fungi are divided into the Ascomycetes (having ascospores), the Basidiomycetes (having basidiospores), the Phycomycetes (having sexual reproduction that does not involve either ascospores or basidiospores), and the imperfect fungi, that have no known sexual reproduction.; Many of the fruiting bodies are macroscopic, and are known as mushrooms, toadstools, puff balls, etc. Most fungi are very valuable reducers, but a few are parasitic on plants and the cause of plant diseases.
Fungicide: A pesticide that kills a fungus. Most fungicides are synthetic and are proprietary compounds that are used to control plant diseases, but a few have medicinal, veterinary, and domestic uses.; The most famous, and spectacularly successful fungicide was Bordeaux mixture, discovered by Millardet in France in 1882.; A protective fungicide is one that is entirely external and which prevents infection. It thus protects the host plant from disease. A systemic fungicide is one that is absorbed by the plant and can kill an internal fungus. It thus cures a disease.
Fusarium oxysporum: This fungus causes wilt diseases in many different hosts. The pathologically induced wilt is usually caused by a combination of xylem vessels that are blocked by the presence of the fungus, and by toxins produced by the fungus.; This fungus has a very wide host range and its various formae speciales are usually named after their hosts, or the area of their first discovery.; Thus f.sp. cubense causes Panama disease of banana, f.sp. albedinis causes Bayoud disease of date palms, f.sp. lycopersici causes tomato wilt, f.sp. apii causes celery wilt, f.sp. conglutinans causes cabbage yellows, f.sp. dianthi causes carnation wilt, f.sp.lini cause flax wilt, f.sp. pisi cause pea wilt, f.sp. vasinfectum causes cotton wilt, and so on.; Amateur breeders can accumulate horizontal resistance in the annual hosts but crops such as banana and date palm are definitely not recommended for them.; Note that the various f.spp., of this fungus exhibit a differential interaction with their host species, but that this differential interaction is not due to vertical resistance. See also: Verticillium.
FYM: See: Farmyard manure.

Glossary: G

Gaia hypothesis: The hypothesis developed by James Lovelock that postulates that the entire biosphere is a single, self-organising, non-linear system.
Gall: An abnormal plant growth, usually more or less spherical, and usually induced by a plant parasite.
Gamete: A sexual haploid cell that may be from either a male or a female, and which unites with another gamete from the opposite sex to produce sexual recombination in a zygote, which is diploid. In plants, the male gametes are called pollen, and the female gametes are ovules.
Gametic sterility: Sterility that results from the fact that either the male or the female gametes are infertile.
Garcinia mangostana: The mangosteen. A delicious fruit native to S.E. Asia. The plant is a dioecious tree, and the seeds are parthenogenetic. Not recommended for amateur breeders.
Garlic: See: Allium sativum.
Gaümannomyces graminis: Previously called Ophiobolus graminis, this fungus causes ‘Take-all’ disease of wheat and other cereals.
Gaussian curve: The bell-shaped curve of a normal distribution.
Gene: The unit of inheritance which is carried on a chromosome. An inherited character may be controlled by a single gene (i.e., a Mendelian gene), or it may be controlled by many genes (polygenes). See also: Allele.
Gene banks: The popular term for collections of plants made for purposes of genetic conservation. A gene bank may consist of collection of seeds, which have to be re-grown periodically, or of an arboretum of tree crops.
Gene frequencies: Mendelian breeding emphasises single genes, and gene-transfers by pedigree breeding.; Biometricians’ breeding emphasises polygenes, and changes in their gene frequencies by population breeding, recurrent mass selection and transgressive segregation.; For example, horizontal resistance is a polygenic character, and its level can be increased by increasing the frequency of its polygenes in a single individual.
Gene pool: The totality of genes possessed by a population of sexually reproducing organisms.
Gene-for-gene relationship: A gene-for-gene relationship exists when each gene for resistance in the host has a corresponding (or matching) gene for parasitic ability in the parasite. The gene-for-gene relationship was discovered by H.H. Flor in 1940.; This phenomenon is the definitive characteristic of the term vertical, and the concept of the vertical subsystem. When the host and parasite genes match, the vertical resistance does not operate, the infection is successful, and parasitism occurs. When the genes do not match, the vertical resistance functions, the infection is unsuccessful, and parasitism does not occur.; The sole function of the gene-for-gene relationship is to control the population explosion of an r-strategists parasite, which usually has an asexual reproduction that leads to a particularly rapid multiplication. This control is commonly achieved by reducing the proportion of allo-infections that are matching infections. But it can also function by reducing the growth, and hence the reproduction, of a non-matching parasite (see quantitative vertical resistance).; A gene-for-gene relationship will evolve only in a discontinuous pathosystem, and in seasonal host tissue (i.e., annual plants, or the leaves and fruit of deciduous trees or shrubs).; For mathematical reasons, it is thought that all individuals of both host and parasite in a wild plant pathosystem have half of the total genes available. This provides the maximum heterogeneity, and the maximum effectiveness, for a given number of pairs of genes in a system of biochemical locks and keys (see n/2 model).
General systems theory: The general systems theory concerns the properties that systems have in common. It is often helpful to study a system in terms of this theory, and in terms of other systems.; There are many different kinds of system, such as solar systems, political systems, ecological systems (ecosystems), mechanical systems, legal systems, electrical systems, and so on. The concept of the pathosystem is based on the general systems theory.; Systems theory is now divided into the general systems theory and complexity theory, which developed out of it. Systems theory is based on the concept of a pattern, and of systems levels, which are patterns of patterns. Thus a book is a pattern of chapters, each of which is a pattern of paragraphs, and so on down to words and letters.; In biology, a population is almost synonymous with ‘systems level’. Thus a forest is a population of trees, a tree is a population of leaves, a leaf is a population of cells, and so on.; Key aspects of systems theory involve the concepts of suboptimisation, emergent properties, and the holistic approach.; See also: Complexity theory, Linear systems, Non-linear systems.
Generation: A plant generation is generally considered to be the life span starting from seed and extending to the next production of seed.; Some annual plants produce up to five generations per year. At the other extreme, some trees require many decades to complete a single generation.; In plant breeding, one breeding cycle may embrace several plant generations, such as a multiplication generation, and selfing generations for single seed descent and late selection.
Genetic advance: The increase in the level of a quantitative variable that results from recurrent mass selection. For example, after one screening generation, there might be a 5% increase in the yield, or in the level of horizontal resistance to a particular species of parasite.
Genetic base: The totality of polygenes at the start of a population breeding program.; Consider a simplified model. Ten parents each possess 10% of the polygenes controlling horizontal resistance. Each parent is thus very susceptible, and the parent population is also very susceptible. But each parent possesses polygenes that no other parent possesses. This means that the genetic base contains 100% of the polygenes controlling horizontal resistance.; The purpose of the population breeding is to bring all these polygenes together in one individual by recurrent mass selection and transgressive segregation.; In practice, some 10-20 different parents, consisting of modern cultivars, preferably originating from independent breeding programs, will normally provide an adequate genetic base for a horizontal resistance breeding program. If the base proves to be inadequate, it can always be widened at a later stage by adding new parents to it.
Genetic code: The system of genetic information storage in DNA and RNA molecules in living organisms. The genetic code is analogous to writing, as a method of storing information.
Genetic conservation: The preservation of genetically controlled characters in gene banks, which consist either of stored seeds, or of living museums in botanic gardens and arboretums.; The concept of genetic conservation was first developed by Mendelians with respect to vertical resistance genes. It is of relatively minor importance for biometricians, and polygenically inherited characters such as horizontal resistance.; However, the conservation of old cultivars is of considerable importance to organic farmers, at least until such time as superior, new, horizontally resistant cultivars become available.
Genetic diversity: Genetic diversity means that the individuals within a population differ in their inherited attributes.; Wild plant populations are typically diverse. Most subsistence crops in tropical countries are also diverse. But modern commercial crops usually have genetic uniformity.; A genetically diverse population has genetic flexibility. A fundamental ecological principle states that diversity leads to stability.
Genetic engineering: A technique that makes it possible to change the genetic make‑up of an individual or species, by introducing a gene from a different species. Of necessity, this technique can work only with single-gene characters, and its scientific popularity is responsible for much of the regrettable neglect of the far more important many-gene (polygenic) characters.
Genetic flexibility: A genetically diverse population has genetic flexibility in the sense that it can respond to selection pressures.; For example, if a host population has too little horizontal resistance, it will gain resistance. This happens because resistant individuals, being less parasitised, have a reproductive advantage over susceptible individuals that are more heavily parasitised.; Both the proportion of resistant individuals, and the levels of resistance (see transgressive segregation), will be increased accordingly in the next generation.; See also: Genetic inflexibility.
Genetic homeostasis: The tendency of a population to maintain a genetic composition that provides an optimum balance with its environment. See also: Homeostasis.
Genetic inflexibility: Most modern cultivars are either pure lines or clones, and they are genetically inflexible in the sense that they do not respond to selection pressures during cultivation. This is a valuable characteristic because it ensures that useful agricultural properties are not lost.; See also: Genetic flexibility.
Genetic line: A line of descent in which each generation is descended from, and related to, the previous generation.
Genetic male sterility: See: Male sterility.
Genetic modification: A term used by molecular biologists to describe the results of genetic engineering. It is an unfortunate choice of words, which is best avoided, because any form of breeding constitutes genetic modification.
Genetic source of resistance: Mendelian breeders working with single-gene resistances must first find a genetic source of resistance, usually in a wild progenitor.; This concept has been so pervasive that many believed the only way to breed for horizontal resistance was to first find a source of resistance. This is incorrect, as polygenic characters cannot be transferred in the way that single-gene characters are transferred, either by back-crossing or by genetic engineering.; Breeding for horizontal resistance involves changing gene frequencies, and this can be achieved with susceptible parents using recurrent mass selection, provided that the genetic base is wide enough.
Genetic uniformity: A genetically uniform population in which all the individuals are identical.; Such a population lacks genetic flexibility in the sense that it cannot respond to selection pressures. For example, if a genetically uniform host population has too little horizontal resistance, it cannot gain more resistance, because all the individuals have an equal level of resistance, and are equally parasitised. No individual has a reproductive advantage over any other individual and, consequently, there will be no change in the level of resistance in the next generation. See also: Genetic flexibility.; Genetic uniformity means that all the individuals within a population are identical in one or more of their inherited attributes. Modern crops are typically uniform because they are cultivated as pure lines, hybrid varieties, or clones. A genetically uniform population has genetic inflexibility and this is desirable in agriculture because it ensures that valuable characteristics will not be lost.; See also: genetic diversity.
Genetically modified organism (GMO): Any organism that had been modified by genetic engineering. The organisms involved range from micro-organisms modified to produce complex pharmaceuticals, to herbicide-resistant and parasite-resistant crops, and pigs intended to provide transplant organs for humans.
Genetically modified pharmaceuticals: Some rare pharmaceutical products can be produced in quantity by genetically modified micro-organisms, and this is a more acceptable application of genetic engineering that the use of GMOs in agriculture. This is because no alternatives to these often essential drugs exist, and the patient either takes them or does without. Even if these drugs did have long-term adverse effects, this is usually considered less damaging to the patient than having no drugs at all. In comparison, there is much less justification for the use of genetically modified crops in agriculture.
Geneticist: A scientist who studies genetics. Plant and animal breeders are often called applied geneticists.
Genetics: The study of biological inheritance. There are two branches of genetics called the Mendelian and the biometrical.; Mendelians study single-gene characters, which are either present or absent with no intermediates.; Biometricians study many-gene (polygenic) characters, which are continuously variable between a minimum and a maximum.; Some scientists recognise a third branch called population genetics, which studies the changing frequencies of Mendelian genes within a natural population. However, this term should not be confused with the very different population breeding.; Obviously, a good geneticist studies all aspects of genetics equally. Plant and animal breeding are sometimes described as applied genetics.
Gene-transfer breeding: See: Pedigree breeding.
Genome: The monoploid set of chromosomes which, in a homozygous plant, occurs in a gamete, and consists of all the genes. A term often used loosely to mean the complete set of genes in a plant.
Genotype: The genetic constitution of an organism, as opposed to its actual appearance, which is called the phenotype. The distinction allows for recessive genes and polygenes, which may be present but not expressed because of heterozygosity.
Genus: In the taxonomic hierarchy, a genus is a subdivision of a botanical family, and it normally constitutes a number of species. A genus is group of closely related species, which have clearly defined characteristics in common.; All plants have two Latin names; the first is the generic name, and the second is the specific name. The adjectival form is ‘generic’, as in inter-generic hybrid.
Geometric series: The series 2⁰, 2¹, 2², 2³, etc., with arithmetic values 1, 2, 4, 8, etc., is a geometric series. This series is relevant to the Habgood nomenclature, and the Person-Habgood differential interaction.
Geotropism: The response of a plant to gravity. A tap root exhibits positive geotropism, and grows downwards. An apical shoot exhibits negative geotropism, and grows upwards.
Germ tube: The microscopic tube, extruded by either a pollen grain or a fungal spore, that penetrates the stigma or the host tissues, as the case may be.
Germination: The first step in the growth of either a seed or a spore.
Germination percentage: A seed testing term which defines the viability of a seed lot.
Gherkins: See: Cucumis sativus.
Gibberellic acid: Also known as gibberellin, this compound was originally isolated from a fungus (Gibberella fujikuroi) but is now known to occur in all plants.; Many different gibberellins, called GA₁, GA₂, etc., have been identified. Gibberellins are plant growth substances that tend to affect the entire plant.; They stimulate growth and have many commercial applications such as breaking potato seed tuber dormancy, increasing celery stalk length, suppressing seed formation in grapes, increasing the size of ornamental flowers, and delaying fruit maturity.
Ginger: See: Zingerber officinale.
Globodera rostochiensis: A cyst-forming nematode, known as the ‘golden nematode’, that is a serious pest of potatoes and tomatoes.
Glomerella spp.: A poorly defined genus of fungi, which are often the perfect (i.e., sexual) stages of Colletotrichum.
Gluten: The main protein in wheat flour. Gluten allows wheat dough to stretch and this makes the production of bread possible, by allowing gas bubbles to develop in the dough from fermentation by yeast.
Glycine max: The soybean, now the most important grain legume in the world, with Brazil, USA, and China being the largest producers.; Soybean was domesticated in China about one millennium BC. However, the modern expansion in cultivation came only after breeding in the USA had produced types suitable for mechanical harvesting and with appropriate day-length responses, because photoperiod sensitivity limits a cultivar to a narrow belt of latitude.; Modern production is as an industrial crop for edible oil extraction (20-23% of the seed) and a high protein meal used mainly for animal feed, but with increasing prospects for human food. In the Far East, soybeans are utilised as soy sauce, soya milk, bean curd or tofu, and green beans. Soybeans can also be used as a pasture crop, and for hay and silage.; Soybean is self-pollinated. About 1% of natural cross-pollination occurs and can be utilised in a recurrent mass selection program if a suitable marker gene can be found. amateur breeders should aim primarily at horizontal resistance, with a view to producing cultivars for organic farmers.
Glycyrrhiza glabra: Liquorice. A pernnial herb of the family Leguminosae, which is of ancient cultivation in Central Asia and Southern Europe. It has sweet rhizomes and roots. The sweetness comes from glycyrrhizin.
GMO and GM: See: Genetically modified organism.
Golden gram: See: Phaseolus aureus.
Golden nematode: See: Globodera rostokiensis.
Gooseberry: See: Ribes grossularia.
Gossypium spp.: Cotton. This genus has about thirty species that are divided into linted and non-linted species.; The four linted species in cultivation are divided into Old World and New World cottons. The two Old World cottons are diploid and are Gossypium arboreum and G. herbaceum. The two New World cottons are tetraploid and are G. barbadense and G. hirsutum. The last of these is Upland cotton and is responsible for about 95% of world production. The long staple Sea Island and Egyptian cottons are G. barbadese and account for about 5% of world production.; Cotton is naturally cross-pollinated, but it is tolerant of inbreeding and inbred cultivar can be maintained. population breeding presents no difficulties.; Since the first use of DDT, cotton has suffered a major vertifolia effect with respect to its insect pests. The increased susceptibility has been aggravated by the boom and bust cycle of insecticide production, and the tendency for politicians and bankers to interfere in the cultivation of the crop.; Population breeding for horizontal resistance in cotton is likely to produce unexpectedly promising results. However, cotton breeding is somewhat technical, particularly in assessing fibre yield and quality, and it should perhaps be undertaken by university breeding clubs.
Gourds: See: Cucurbitaceae.
Gradient: See: Parasite gradient.
Grafting: The technique in which a scion is biologically joined to a stock.; The stock is usually a horizontally resistant rootstock, and this provides a means of controlling root and trunk diseases. The scion is usually a high quality but susceptible cultivar.; The classic example of this control method was the grafting of classic wine grapes on to American rootstocks in order to control Phylloxera.; Occasionally, a double graft is used, as with a susceptible rubber trunk being grafted to both resistant rootstocks and leaf blight-resistant crowns. Other uses of grafting include the grafting of potato parents on to tomatoes to produce a vine with many inflorescences for use in true seed production.; There are two general techniques of grafting. A bud graft involves inserting a bud of the scion under the bark of the stock, and is the usual method for tree crops. A wedge graft involves inserting a wedge of the scion into a V-slit cut into the stem of a decapitated stock, and is the usual method for herbaceous plants.; A third technique is the ‘approach’ graft in which the cut surfaces of the stems of two separately rooted plants are bound together, but it is rarely used.
Grain crops: This term covers all crops in which the harvestable product is a small seed. It includes all the cereals, the grain legumes, the pseudo-cereals, and mustard.; However, oil seed crops, such as sunflower, flax, and canola, are not normally considered to be grains.
Grain Legumes: See: Leguminoseae.
Gram: See: Phaseolus.
Gramineae: The grass family. Cultivated members of this Monocotyledonous family include the cereals, fodder grasses, and sugarcane. According to some taxonomists, the bamboos are also members of this family.; There are about 8,000 species of grass in some 700 genera. From the human point of view, this is quite the most important family of plants as it provides most of our food, either directly or indirectly (all beef is grass).
Gram-positive: A staining test used in the identification of bacteria. The bacteria are stained with crystal violet and then iodine. They are then washed in a solvent such as acetone or alcohol. Gram-positive bacteria retain the stain, while gram-negative bacteria lose it.; All plant pathogenic bacteria are gram-negative, except Corynebacterium spp.
Granadilla: See: Passiflora edulis.
Grapes: See: Vitis vinifera.
Grapefruit: See: Citrus paradisi.
Grassland: Most grasslands are natural, and sown grassland (pasture) is a relative new concept in agriculture. Natural grasslands are known variously as savannah, prairie, pampas, scrub, veldt, chaparral, and steppes.
Grass: Any member of the botanical family Gramineae. This family includes the cereals, the fodder grasses, sugarcane, and, according to some taxonomists, the bamboos.
Green manure: A crop grown specifically for improving the soil by being ploughed into the soil while still green. Green manures often consist of legumes which fix nitrogen.
Green pea: See: Pisum sativum.
Green Revolution: The Green Revolution resulted from the development of dwarf wheats and rices that could tolerate heavy applications of nitrogenous fertiliser without lodging. This led to major increases in the world production of food and earned Norman Borlaug a Nobel Peace Prize in 1970.
Greenhouse: Both glass and plastic film are transparent to light but opaque to radiant heat. A greenhouse absorbs sunlight which is re‑radiated internally as heat.; Temperate greenhouses have the problem of inadequate sunlight during winter and at night, and they have to be artificially heated.; Tropical greenhouses have the problem of excessive heat, and they have to be cooled. Refrigeration is prohibitively expensive, and the best cooling is by good ventilation that evaporates large amounts of water.; Greenhouses also protect plants from rain and hail, and they can be fumigated.; Commercial greenhouses are used for producing crops out of season. In plant breeding, research greenhouses are used mainly to reduce the length of the breeding cycle by increasing the number of plant generations in one year.
Greenhouse cooling: The cooling of a plant breeding greenhouse in hot seasons can be difficult. The external surface of the glass or plastic can be sprayed with a heavily diluted white plastic emulsion paint in order to reduce the light absorption. Rapid changes of air, by extraction fan if possible, and the evaporation of large amounts of water, offer the most efficient and the most economical cooling. Refrigeration is far too expensive.
Greenhouse effect: This is a geophysical effect, in which the so-called greenhouse gasses (i.e., carbon dioxide, methane, etc.) in the atmosphere are transparent to sunlight but opaque to radiant heat. This phenomenon is believed to lead to global warming.
Greenhouse gasses: See: Greenhouse effect.
Greenhouse screening: Screening a breeding population inside a greenhouse. Because of the requirements of on-site selection, greenhouse screening is inadvisable, except when breeding a crop that is to be cultivated in a commercial greenhouse. However, other components of the breeding cycle (e.g., multiplication, single seed descent, pollination) may be undertaken out of season in a greenhouse in order to reduce the total breeding time.
Gregarious: Growing or living in groups. Gregarious plants grow in closely-spaced clumps; gragarious insects tend to clump together and so do not cause evenly-distributed crop damage. This is important to note while screening for horizontal resistance.; See also: Sociability scale, Patchy distribution
Grid screening: Grid screening is a technique for overcoming parasite gradients and patchy distributions of parasites, in field screening. The entire screening population is divided into a grid of suitably sized squares, and relative measurements are used to select the best individual in each square. Squares that are totally free of a parasite should be eliminated from the screening process.
Gros Michel: The most popular cultivar of banana during the first half of the twentieth century. It eventually went out of production because of the new encounter Panama disease. Nevertheless, the continuous monoculture of a single clone, for half a century, over a huge area in the tropics, where there is no closed season, was a remarkable indication of the possibilities of horizontal resistance.
Groundnut: See: Arachis hypogea.
Groundnut, Bambara: See: Voandzeia subterranean.
Growth chamber: A special chamber with controlled light, heat, humidity, and atmosphere, for conducting research into plant growth. These chambers are often useful when studying crop parasites, but they are expensive, and are not normally necessary for amateur breeders.
Grub: The larval stage of many insects, including many crop parasites.
Guano: Semi-fossilised excrement of fish-eating birds. Guano was much prized as a source of natural phosphate but is now in short supply.
Guar: See: Cyamopsis tetragonolobus.
Guava: See: Psidium guajava.
Guignardia bidwelli: An Ascomycete fungus that causes black rot of grapes.
Guinea corn: See: Sorghum.
Gumbo: The West African name for okra, Abelmoschus esculentus.
Gum trees: See: Eucalyptus spp.
Guttation: The excretion of water by plants, usually at night, when atmospheric humidity is high, and transpiration is restricted. Typically, this makes lawns wet in the early morning. This wetness is often mistakenly called dew. A true dew is caused by condensation of water from a saturated atmosphere.
Gymnosperm: Seed forming plants whose seeds are not protected by a seed coat. This group includes the conifers, cycads, yews, and Ginkgo. Gymno- is Greek for naked, and the name Gymnosperm has the same root as gymnasium.
Gymnosporangium: A genus of rust fungi, in which most species are heteroecious, with the summer stage mainly on Cupressus spp., and the winter (sexual) stage on pome fruits.

Glossary: H

Habgood nomenclature: This nomenclature uses the numbers of the binomial expansion (i.e., 2⁰, 2¹, 2², 2³, etc., with arithmetic values of 1, 2, 4, 8, etc.). Each binomial number has an arithmetic value that is double that of its predecessor. The sum of any combination of binomial numbers is unique. For example, the sum 21 can be obtained only by adding 16 + 4 + 1, and no other combination of binomial numbers can add up to this sum.; The nomenclature can be applied to matching pairs of vertical genes. Each pair of matching genes is then labelled with the binomial numbers 1, 2, 4, 8, etc., in order of discovery. The name of each pair of genes is the primary Habgood name, and it is a single binomial number. Any combination of genes is named with the sum of their binomial numbers, and this is a secondary Habgood name.; Any combination of genes, in either the host or the parasite, is named with a single number, and exactly matching vertical resistances and vertical parasitic abilities have the same name.; The composition of a secondary Habgood name is easily determined. Suppose the secondary name was 29. The largest possible binomial number is subtracted from it. In this case, this would be binomial 16. This means that gene 16 is present. The remainder is 13, from which 8 can be subtracted, indicating that gene 8 is present. The remainder is now 5, showing that genes 4 and 1 are also present. These gene names 16 + 8 + 4 + 1 add up to 29, and no other combination of binomial numbers can add up to this sum.
Habitat: The natural home of an organism, usually with living conditions that are closely similar to those of its original environment.
Hand-pollination: The artificial pollination of a flower, usually involving cross-pollination in order to obtain a sexual recombination of two chosen parents. See also: Emasculation.
Haploid: A cell or plant that has only one set of chromosomes. A sex cell (i.e., pollen and ovules in plants, sperm and ova in animals) is normally haploid, and the fusion of two sex cells produces a normal diploid with two sets of chromosomes. Haploid plants can be produced artificially, and their single set of chromosomes can be doubled to produce a doubled monoploid. The terms haploid and monoploid are synonymous. See also: tetraploid, triploid.
Hardy-Weinberg law: The law that states that gene frequencies will remain constant from generation to generation, provided that no other factors, such as selection or mutation, are operating.
Hardwoods: Timber trees that are Dicotyledons. The timber of these trees is suitable for fine furniture and cabinet making. See also: Softwoods.
Haricot bean: See: Phaseolus vulgaris.
Harvesting: The process of gathering in a crop. Commercial harvesting of grain crops is usually undertaken with a combine harvester. Many horticultural crops, and all subsistence crops are harvested by hand. The harvesting of a plant breeder’s screening population usually involves carefully selected individual plants.
Hashish: See: Cannabis sativa.
Hay: Pasture grasses and/or pasture legumes that have been cut and dried in the field for use as animal feed. “Making hay while the sun shines” is a traditional method of providing winterfeed for farm livestock.
Hazel nut: See: Corylus avellana.
Head to row selection: See: Family selection.
Hectare: A measure of land area. One hectare is 10,000 square metres, or 2.471 acres.
Helianthus annuus: The sunflower, which is now a valuable oil crop. The Church in Russia forbade the use of a long list of cooking oils on many fast days each year. Being an unknown New World plant, sunflower was not on that list of proscriptions. It consequently became very popular in Russia where the first cultivars were developed. Dwarf varieties are now grown for combine harvesting in many countries. The species is open-pollinated and amenable to selection for horizontal resistance by amateur breeders Sunflowers, and the closely related Jerusalem artichoke, are the only crop species of any significance to originate in North America.
Helianthus tuberosus: The Jerusalem artichoke. A close relative of the sunflower, it is open-pollinated and amenable to recurrent mass selection for horizontal resistance by amateur breeders who might have a special interest in this rather unimportant crop.
Heliotropic: (= phototropic) A directional growth or movement towards light.
Helminthosporium: A genus of fungi which cause disease on a number of crops. While mostly imperfect fungi, a few species belong to the Ascomycete genera Pyrenophora, Ophiobolus, Gaeumannomyces, and Cochliobolus.
Hemileia vastatrix: Coffee leaf rust. This disease is of interest because, when arabica coffee was taken as one pure lines to the New World, all of its pests and diseases were left behind in the Old World. This gave Latin America a commercial advantage and it now produces about 80% of the world’s coffee. When the rust was accidentally introduced into Brazil in 1970, there were fears of a major disruption of the world supply. Fortunately these fears proved groundless, as the disease was easily controlled.; Leaf rust is also interesting in that its spores can be either wind-borne or water-borne. The former method of dissemination is clearly for the process of allo-infections from tree to tree. The latter is for Auto-infection from one leaf to another within one tree.; This disease is an apparent exception to the rule that vertical resistance will evolve only in the seasonal tissue of a discontinuous pathosystem, because coffee is an evergreen perennial. However, infection can only occur if there is free water on the leaf surface. During the tropical dry season, all infected leaves are shed, and the fungus dies with them. Consequently, arabica coffee is functionally deciduous with respect to rusted leaves only.
Hemiptera: An order of insects usually called ‘bugs’. Many leaf bugs are important crop pests. The order also includes the bed bug, which is of interest in demonstrating the stability of natural pyrethrins.
Hemp: See: Cannabis sativa.
Hemp, Deccan: See: Hibiscus cannabis.
Hemp, Manila: See: Musa textilis.
Hemp, sunn: See: Crotalaria juncea.
Herb: Any flowering plant that lacks woody tissues.
Herbicide: Any chemical that kills weeds. Modern herbicides are often selective in the sense that they will kill some types of plant but not others. Typically, 2,4-D kills Dicotyledons and may be used safely on Monocotyledons crops such as cereals. Further selectivity has been obtained by the use genetically modified crops that are resistant to a specific herbicide.
Herbicide injury: Traces of herbicide in sprayers or other equipment can cause injuries to crop plants. The symptoms can be very confusing and, if suspected, a specialist should be consulted.
Herbivores: An animal that lives on plants, mostly grasses that can withstand grazing because their leaves grow from the base, and not the tip. The appearance of grasses, some 25 million years ago, led to an explosive evolution of herbivores. The evolution of humans, as hunter-gatherers, depended on the fact that the African savannah carries up to 20,000 kilograms of herbivores per square kilometre. At the other extreme, tropical rain forest carries only 5-10 kg/sq.km. It is no accident that rain forests have the fewest archaeological remains of hunter-gatherers, or that our hominid ancestors favoured open grasslands.
Herders: Nomadic people who had domesticated a social (i.e., herding) species of animal. Surviving herder societies include the Laplanders who herd reindeer, and the Masai, who herd cattle. The earliest known herders date from 20,000 years ago, and they herded Barbary sheep in North Africa.
Heritability: The percentage of a plant’s quantitative variable that is due to genetics, the remaining percentage being due to environment. For example, a plant may have a zero level of parasitism because the parasite is absent from the area in question. It appears to have 100% resistance. However, if the parasite were present with maximum epidemiological competence, the plant might have a 50% level of parasitism. The heritability of that apparent 100% resistance would then be only 50% (i.e., half of the original apparent resistance is inherited and can be inherited by the progeny, while the other half is an environmental effect that cannot be transmitted to the progeny).
Hermaphrodite: Having both sexes in one individual. In plants, this means having both sexes in one flower. If both sexes occur in separate male and female flowers on one plant, this arrangement is termed dioecious. See also: monoecious.
Hessian fly: See: Mayetiola destructor.
Heteroecious: Greek = different houses. A heteroecious plant parasite is one that is compelled to parasitise two different species of host, often called the winter host, during which sexual recombination occurs, and the summer host, which involves asexual reproduction only, in order to complete its life cycle. A heteroecious pathosystem has two species of host.; In practice, the only heteroecious parasites of plants are species of aphids and rusts, but some of them are major pests and disease of crops. During the summer phase, these parasites are r-strategists and a system of biochemical locks and keys, derived from the vertical subsystem and the gene-for-gene relationship, can be shown to have a remarkable evolutionary survival advantage.
Heterogeneous: Of different descent (c.f., heterogenous = of different composition). Pronounce it heterogeneous (c.f., heterogenous). See also: homogeneous, homogenous.
Heterogenous: Of different composition (c.f., heterogeneous = different descent). Pronounce it heterogenous (c.f., heterogeneous). See also: homogeneous, homogenous.
Heterosis: The hybrid vigour that is exhibited by the progeny of two inbred (i.e., homozygous) but different parents. This vigour persists for only one generation, and it is the basis of hybrid varieties.
Heterozygous: This term refers to a plant whose two parents were genetically different. In plants, the term may refer to a single gene, or to the entire genetic makeup of the individual plant. Heterozygous plants do not ‘breed true to type’. See also: homozygous.
Hevea brasiliensis: Para rubber. Note that the name comes from the State of Para in Brazil, and that each ‘a’ is pronounced long, as in ‘art’. The name should not be pronounced with a short ‘a’ as in ‘parachute’.; Para rubber is a deciduous tree native to the Amazon Valley. It was taken to the Far East by the British, and this area became the main producer because it was free of the native pests and diseases. The Brazilian complaint that rubber was stolen from them is not justified in view of their enormous use of Old World crops such as coffee, sugarcane, and soybean.; In any event, plantation rubber does not thrive in Brazil, but old plantations, laid out by the Ford Motor Company in the early part of the twentieth century, have survivors that are resistant to disease and these merit screening for vegetative propagation.
Hexaploid: A cell or a plant with six sets of chromosomes. Diploid is the normal state in most plants and animals. See also: doubled monoploid, haploid, tetraploid, triploid.
Hibiscus cannabis: Kenaf, bimli jute, or Deccan hemp. A jute substitute that probably originated in Africa.
Hibiscus esculentis: See: Abelmoschus esculentus.
Hippomane manchinella: This is the plant from which arrowhead poisons are extracted in South America. It is of interest in that arrowroot got its name from being a supposed antidote to these poisons.
Holistic approach: A systems term meaning that systems analysis, or systems management, is being conducted at the highest feasible systems level. The converse, in which the system is studied at the lower systems levels, is called the merological approach. The holistic approach is essential if suboptimisation is to be avoided.
Homeostasis: The ability of a system to maintain an optimum in all its variables, and to recover from swings away from this optimum, at any systems level. The recovery is the result of negative feedback. For example, if people get too hot, they sweat, and the evaporation of the sweat cools them down. Conversely, if they get too cold, they shiver, and this unconscious exercise warms them up. See also: Genetic homeostasis.
Homogeneous: Of the same descent (c.f., homogenous = of same composition). Pronounce it homogeneous (c.f., homogenous, as in homogenised milk). See also: heterogeneous, heterogenous.
Homogenous: Of the same composition (c.f., homogeneous = same descent). Pronounce it homogenous, as in homogenised milk, (c.f., homogeneous). See also: heterogeneous, heterogenous.
Homologous evolution: Evolution in which similar features have a common origin (e.g., all the plants in one family have a common ancestor). This is in contrast to analgous evolution, in which similar features have different origins (e.g., the wings of birds, insects, and bats represent analogous evolution).
Homozygous: In plants, this term may refer to the alleles of a single gene, or to the entire genetic makeup of an individual plant. In the former situation, the two parents each had the same allele of that gene. In the latter situation, the two parents were genetically identical in all respects. A population of plants that are homozygous in their entire genetic makeup is called a pure line, and these plants ‘breed true to type’. (See also: heterozygous).
Hops: See: Humulus lupulus
Hordeum vulgare: Barley. A crop that is as old as wheat, dating from about nine thousand years ago. It is salt-tolerant, and it often substituted for wheat, in ancient times, in soils that had become salty from inappropriate irrigation. However, it is little used in human nutrition today. The main use is for animal feed, and for malting to make beer. There is plenty of scope for developing horizontal resistance, and the crop is probably amenable to the use of male gametocides.
Horizontal: In a plant epidemiological context, this term is entirely abstract, and it means that a gene-for-gene relationship is absent. Horizontal resistance and horizontal parasitic ability are both defined by the absence of a gene-for-gene relationship. A horizontal subsystem of a pathosystem is also defined by the absence of a gene-for-gene relationship.; See also: Horizontal parasitic ability, horizontal resistance, Horizontal pathotype, and Horizontal pathodeme.
Horizontal parasitic ability: Parasitic ability that does not result from a gene-for-gene relationship. Horizontal parasitic ability is the parasitic ability of the Biometricians, and its inheritance is usually controlled by many polygenes. Although it has been very little studied, it seems always to vary quantitatively. It is the parasitic ability that enables a parasite to obtain nutrients from its host after the vertical resistance has been matched, and in spite of the horizontal resistance. (See also: vertical parasitic ability).
Horizontal pathodeme: A population of a host in which all individuals have the same horizontal resistance. Many different cultivar with the same horizontal resistance, but with differing agronomic characteristics, all belong to the same horizontal pathodeme.
Horizontal pathotype: A population of a parasite in which all individuals have the same horizontal parasitic ability. The various members of a horizontal pathotype may differ in other respects, such as pesticide resistance.
Horizontal resistance: Resistance that does not result from a gene-for-gene relationship. Horizontal resistance is the resistance of the Biometricians; its inheritance is normally controlled by polygenes.; It results from many different resistance mechanisms; it is quantitative in both its inheritance and its effects; it controls all the consequences of a matching infection including Auto-infection; it also controls allo-infections in a continuous pathosystem that lacks a gene-for-gene relationship; and it is durable resistance.; The level of horizontal resistance can be at any degree of difference between the minimum and the maximum. The minimum level of horizontal resistance usually means that there is a total loss of crop in the absence of crop protection chemicals. Conversely, the maximum level of horizontal resistance usually means that there is a negligible loss of crop in the absence of crop protection chemicals.; In plants that don't have a gene-for-gene relationship, horizontal resistance is the sole protection, and the only resistance. In plants that have a gene-for-gene relationship, the function of horizontal resistance is to control all the consequences of a matching allo-infection, including all auto-infection. So horizontal resistance occurs in every plant against every parasite of that plant.; Horizontal resistance requires population breeding and recurrent mass selection. For this reason, Mendelian breeders do not like it, and it has been seriously neglected during the twentieth century. However, these population breeding techniques are so easy to use in most crops that amateur breeders can breed for horizontal resistance, especially with the support of OPBF or another plant breeders association.; Once adequate horizontal resistance is accumulated, the environmental and human hazards, as well as the labour and costs of applying crop protection chemicals are eliminated.; Because a good horizontally resistant cultivar never needs to be replaced, except with a better cultivar, breeding for horizontal resistance is cumulative and progressive.; As horizontal resistance is accumulated, the crop losses from pests and diseases decline, and the biological anarchy that was induced by the use of crop protection chemicals also declines, as biological control agents return and increase in numbers.; The improved biological control enhances the effects of the horizontal resistance. The two factors are mutually reinforcing.; See also: Horizontal parasitic ability, vertical resistance, Comprehensive horizontal resistance, Laboratory measurements, Relative measurements, Partial resistance, Field resistance, Race-non-specific resistance.
Horizontal resistance, comprehensive: The horizontal resistance to one species of parasite does not normally function against any other species of parasite. Comprehensive horizontal resistance means that a cultivar has high levels of horizontal resistance to all the locally important species of parasite. This is achieved during breeding by selecting for the one character of ‘good health’ (i.e., the holistic approach).; Because the epidemiological competence of parasites varies considerably between agro-ecosystems, the horizontal resistances that are comprehensive in one agro-ecosystem may be too high, or too low, in another agro-ecosystem. This is why on-site selection is important.
Horizontal resistance, examples: There are numerous examples of deliberate and successful breeding for horizontal resistance. The best summary is by N.W. Simmonds, entitled Genetics of Horizontal Resistance to Diseases in Crops, and published in Biol. Rev. 66: 189-241. See also: Phaseolus vulgaris.
Horizontal resistance, laboratory measurements: Horizontal resistance can be measured in the laboratory using plant growth chambers. But these measurements are expensive and difficult, and they do not necessarily correspond to field performance. They are not recommended for amateur breeders.
Horizontal resistance, opposition to: The scientific opposition to horizontal resistance during the twentieth century was apparently due to the fact that plant breeding was dominated by Mendelian breeders who (1) disliked working with polygenes and population breeding methods, and (2) favoured work with single-gene resistances, in spite of the ephemeral nature of vertical resistance. This attitude, which still endures, has led to a serious vertifolia effect in many crops, and it does much to explain why we now use crop protection chemicals in such enormous quantities. See also: Mindset.
Horizontal resistance, relative measurements: Horizontal resistance is difficult to measure and it has no exact scale of measurement comparable, say, to the Celsius scale of temperature measurement. In practice, the only feasible measurements of horizontal resistance are field measurements that are also relative measurements. That is, a cultivar is described as being either more or less resistant to a specified parasite, than another cultivar of known performance.
Horizontal subsystem: The subsystem of a pathosystem that is controlled by horizontal resistance and horizontal parasitic ability.
Hormone: A substance that regulates the behaviour of specific cells or tissues. Hormones can be natural or synthetic.
Hormone mimic: Some synthetic chemicals, such as insecticides, can mimic hormones and, at extremely low concentrations, they can damage an unborn human foetus, or an actively growing young child. The safest course for an expecting mother, or for young children, is to eat only organic foods.
Horse bean: See: Vicia faba.
Horseradish: See: Armoracia rusticana
Horticulture: That branch of crop husbandry that involves fruits, vegetables, and ornamentals.
Host: A species, or an individual organism, that harbours parasites, and supplies those parasites with nutrients.
Host range: The range of different species of host that a parasite is able to exploit.
Host-parasite relationship: The category of parasitism in which there is a high frequency of parasitism, but a low injury from parasitism. For example, fleas parasitise zebras. They parasitise every zebra in the herd, so the frequency of parasitism is maximal. But they do very little harm to each individual zebra, so the injury from parasitism is minimal. See also: Predator-prey relationship.
Hot water treatment: A treatment for seeds that are infected. With careful control of the temperature, it is possible to kill the pathogen without killing the seed. Loose smuts of cereals can be controlled in this way.
Houseflies: These flies were the first known insects to develop resistance to a synthetic insecticide, which was DDT in Naples, during World War II, thus demonstrating the previously unknown possibility of unstable insecticides.
Humulus lupulus: Hops, which are now used almost exclusively for brewing beer. The plant is a perennial vine which dies back to ground level each fall. The above-ground parts thus have a discontinuous pathosystem and they have vertical resistance.; Hops is a long-day plant and it is dioecious. It is propagated vegetatively, and only about eight clones dominated world production until quite recently. These include ‘Fuggle’ and ‘Golding’ in Britain, ‘Hallertaur’ in Bavaria, and ‘Saaz’ in Czechoslovakia. These clones are mostly ancient, and they demonstrate the utility and durability of horizontal resistance.; A breeding program started in Germany in 1922 accumulated polygenic resistance to downy mildew by breeding within the European population. This was one of the earliest examples of horizontal resistance being chosen over vertical resistance. This is not a crop for amateur breeders.
Humus: The decomposed organic matter in soils. Humus is a source of plant nutrients, and it is necessary for microbiological activity. It also contributes to soil structure and drainage.
Hundred seed weight: This measurement indicates the average seed weight in a crop such as wheat. Breeders who aim exclusively at total yield may end up with very many, very small grains; while breeders who aim exclusively at a high weight of individual seeds may end up with low yields. amateur breeders should be aware of this laboratory measurement when selecting parents in a program of recurrent mass selection.
Hungry Forties: The period during the 1840s when blight was destroying the potato crops of Europe. The famine was at its worst in Ireland where one million people died of starvation, and one and a half million emigrated, mainly to North America. This reduced the population of Ireland by about one third. Eastern Germany, Poland, and western Russia suffered similar famines.
Hunter-gatherers: People who are pre-herders and pre-agriculturalists. Hunter-gatherers still exist in areas where herding and agriculture are not possible (e.g., Kalahari desert). The early vegetarian hominids became tool-users, employing naturally shaped stones to break open large bones abandoned by carnivores. Later they became tool-makers, and this initiated a period of about two million years of hunter-gathering. Herding started only twenty thousand years ago, and agriculture began a mere nine thousand years ago.
Hyacinth bean: See: Lablab niger.
Hyaline: A mycological term that means a tissue which is lacking pigments and is almost transparent.
Hybrid: The offspring of a cross between two different genera, species, or varieties. Note the specialised meaning of hybrid variety.
Hybrid seed: See: Hybrid variety.
Hybrid swarm: A population, usually of an open-pollinated plant, that shows very great genetic diversity because it is derived from a cross between two or more different species. The tea crop is a typical example. See also: cline.
Hybrid variety: A cultivar of an open-pollinated species (e.g., maize, cucumber, onion) which has been produced by crossing two inbred lines. The resulting seed then produces plants that exhibit hybrid vigour, or heterosis. A hybrid variety can be used only once, because the hybrid vigour is largely lost in the second generation. This means that the seed of hybrid varieties is expensive, but the expense is more than justified by the increased yields. Hybrid varieties do not normally need the protection of breeders’ rights because the breeder has complete control of the inbred lines.
Hybrid vigour: Also known as heterosis, this is the increased vigour that is exhibited by an interspecific cross (e.g., mules, which are sterile hybrids of a horse and donkey), or by a cross between two inbred lines of a single species, particularly an open-pollinated species of plant. See also: Hybrid varieties.
Hybridisation: In plants, the cross-pollination that produces a hybrid.
Hydroponics: The cultivation of plants in a nutrient solution instead of in soil. This technique is used mainly in greenhouses, and it is particularly useful for single seed descent. The plant roots can be suspended directly in the solution, or in inert gravel wetted with the solution, or inside flattened, plastic, tubular, film that is lying on the ground. In the last case, the plant grows through a small hole in the film, and nutrient solution is pumped continuously through the tube.; The advantages of hydroponics are (i) a high density of plants using less greenhouse space, (ii) rapid growth and maturation leading to a shortened breeding cycle, (iii) general freedom from pests and diseases, and (iv) labour-saving.; While the vast majority of hydroponics use synthetic fertilizers, it is possible to use organic nutrients. Whether the food produced can be classed as organic depends on local regulations.
Hymenoptera: The Order of insects that includes bees, wasps, ants, and Ichneumons.
Hyperparasite: A parasite of a parasite. One of the principle agents of biological control. For example, rust is a parasite of coffee leaves, and it has a hyper-parasitic grub that eats its spores. If coffee trees are sprayed with insecticides, the effects of this hyper-parasitism are lost. See also: Predator.
Hypersensitive fleck: A small necrotic speck, just visible to the naked eye, which indicates a hypersensitive reaction of a gene-for-gene relationship to a non-matching allo-infection.
Hypersensitivity: The process in which a group of cells surrounding an infection site dies very rapidly, and the infecting parasite dies with them. The infection then fails. This is a common mechanism of vertical resistance against allo-infections in leaves, but note that not all vertical resistance is due to hypersensitivity (e.g., Fusarium and Verticillium wilts), and not all hypersensitivity is due to vertical resistance. See also: Hypersensitive fleck.
Hypha: A single strand of microscopic fungal mycelium.
Hypocotyl: The stem of a germinating seedling that is below the cotyledons.

Glossary: I

IBPGR: The International Board for Plant Genetic Resources, located in Rome, Italy.
ICARDA: The International Centre for Agricultural Research in the Dry Areas, located at Aleppo, Syria. This is one of the CGIAR research stations.
Ichneumon flies: Small wasps belonging to the Hymenoptera, that parasitise other insects by laying eggs in them, in their early instars. These are useful biological control agents.
ICRISAT: International Crops Research Institute for the Semi-arid Tropics, located in Hyderabad, India. This is one of the CGIAR research stations.
IITA: The International Institute for Tropical Agriculture, located at Ibadan, Nigeria. This is one of the CGIAR research stations.
Ilex paraguariensis: Yerba maté. An infusion of the leaves is similar to tea, and is popular in the southern areas of South America.
Immobile nutrients: Immobile nutrients cannot move around in the plant and, consequently, their deficiency symptoms appear first in the young leaves. Immobile nutrients include: Calcium, Boron, Sulphur, Iron, and Copper.
Immunity: Immunity means that a host cannot be parasitised by a particular species of parasite. Thus, coffee is immune to wheat rust, and wheat is immune to coffee rust. Immunity is a non-variable. The maximum level of horizontal resistance may be an apparent immunity, but it is not true immunity because it is variable, and it can be eroded. Vertical resistance has often been called immunity, but it too is an apparent immunity because it operates only against non-matching strains of the parasite.
Impartial resistance: See: Partial resistance.
Imperfect fungus: A fungus that has never been known to produce ascospores, basidiospores, or oospores, and which consequently cannot be classified among the Ascomycetes, Basidiomycetes, or Phycomycetes respectively. The imperfect fungi are also known as fungi imperfecti, the Deuteromycetes, or the asexual fungi, and their reproduction is apparently entirely asexual.
Inbred line: A genetic line of plants that has been self-pollinated for a sufficient number of generations (usually a minimum of six) to produce individuals that are more or less homozygous, and which ‘breed true’. See also: pure lines.
Inbreeder: A species of plant that is autogamous (i.e., self-pollinating). See also: Outbreeder.
Inbreeding cereals: Cereals, such as wheat, rice, barley, and oats that are self-pollinating and are usually cultivated as pure lines.
Inbreeding crops: Many of the cereals and grain legumes are inbreeding and they require hand-pollination during the breeding process. See individual crops for details. Most tree crops are outbreeding, with the notable exceptions of arabica coffee and peach.; Traditionally, during the twentieth century, inbreeding crops have been subjected to Pedigree breeding and the gene-transfer techniques suitable for single-gene characters, rather than the recurrent mass selection that promotes manygene characters. Consequently, many of them exhibit a marked vertifolia effect, and they are mostly good candidates for breeding for horizontal resistance by amateur breeders.
Inbreeding depression: The converse of hybrid vigour, or heterosis. When an outbreeder is repeatedly selfed there is a steady loss of vigour. When two of these inbred lines are crossed, they exhibit heterosis.
Inbreeding grain legumes:: The following grain legumes are inbreeders:; All cultivated species of Phaseolus, Arachis, Cicer, Glycine, Lablab, Lens, Pisum, Psophscarpus, and Voandzeia. See also: Outbreeding legumes.
Incompatibility: When both self and cross-pollination are unable to fertilise, the pollination is described as incompatible. See also: Selfincompatibility.
Incubation period: See: Latent period.
Indeterminate: Some crops, such as haricot beans, can have either the determinate or the indeterminate habit. With the former, they are self-supporting, bushy plants. And with the latter, they grow as vines. Potatoes are determinate plants but, when grafted on to tomatoes, they become indeterminate, and this is a very useful technique when many flowers are needed for the production of true seed for breeding purposes.
Indigenous: This term means that a species is native to the area in question. The converse words are exotic and foreign.
Indigo: See: Indigofera spp.
Indigofera spp.: Several species of this genus of the Leguminoseae are cultivated for a natural blue dye called indigo, or anil. This dye has been used for at least 4000 years, and it is superior to the European woad (Isatis tinctora). However, with the development of analine dyes, the world market for natural dyes collapsed.
Induced deficiencies: Occasionally, a nutrient deficiency can be induced, in spite of the fact that there is an adequate amount of that nutrient available. For example, water softeners replace calcium salts with sodium salts. An excess of sodium salts can induce a potassium deficiency. For this reason, house plants should never be watered with softened water.
Industrial country: The politically correct term for the rich countries of the world. The poor countries used to be called ‘Third World’ countries but are now referred to as non-industrial countries.
Industrial melanism: In Britain, during the industrial revolution, a species of moth, which had superb camouflage colouring when resting on the bark of a tree, became very visible to insect-eating birds when the tree bark turned black from soot pollution. It was shown by breeding experiments that light-coloured moths could easily be changed to black, and vice versa. This is an example of the ability of reversible micro-evolution to change ecotypes.
Infected seed: Infected seed has internal parasites that cannot be reached by surface chemicals which would control contaminated seed. Typically, covered smuts of cereals produce contaminated seed, while loose smuts of cereals produce infected seed.
Infection: In a plant pathological context, this term is defined quite strictly. It is the contact made by one parasite individual with one host individual for the purposes of parasitism. See also: allo-infections, Auto-infection.
Infectious: This term is normally taken to mean that a disease is caused by a parasitic organism, and that it can be transmitted from one host individual to another. But, in common usage, a laugh or a yawn can also be described as infectious.
Infestation: This term is usually used in relation to insects but, in a wide epidemiological context, the terms infection and epidemic can be applied to all categories of parasite, including the insects.
Inflexibility: See: Genetic inflexibility.
Inflorescence: A flowering structure that has more than one flower. For example, the Umbellifereae are so called because each inflorescence is made up of many florets in an arrangement that is reminiscent of an umbrella.
Inheritance: Inheritance is described as monogenic when the character in question is controlled by a single gene. Monogenic inheritance is qualitative in its effects and it leads to discontinuous variation in which a character is either present or absent, without any intermediates. Inheritance is described as polygenic if the character in question is controlled by many genes, called polygenes. Polygenic inheritance is quantitative in its effects, and it exhibits continuous variation with all degrees of difference between a minimum and a maximum. All polygenic resistance is horizontal resistance, but not all horizontal resistance is inherited polygenically.
Initial inoculum: The size of the parasite population at the beginning of the epidemic. Other things being equal, a high initial inoculum leads to a more rapid development of the epidemic, while a low initial inoculum leads to a slower or later development of the epidemic.
Injury: The injury from parasitism is the actual amount of damage done to an individual host, or the average amount done to a host population, by the parasite. The frequency of parasitism is the proportion of host individuals that are parasitised. In a wild plant pathosystem, the injury from parasitism is inversely proportional to the frequency of parasitism. That is, the higher the frequency, the lower the injury, and, conversely, the higher the injury, the lower the frequency. In this way, the total damage from parasitism never exceeds a tolerable level that does not impair the host's ability to compete ecologically and evolutionarily. Vertical resistance, with its system of locking, reduces the frequency of parasitism. horizontal resistance, as a second line of defence, reduces the injury from parasitism. Continuous plant pathosystems, that have horizontal resistance only, usually have a high frequency of parasitism, and a low injury from parasitism.
Inoculation: In a crop science context, this terms means to introduce a parasite to a plant individual or population. Thus a screening population may be inoculated (or artificially infested) with one or more species of parasite in order to exert selection pressure for resistance. See also: Designated pathotype.
Inoculum: The living culture of a parasite that is used to inoculate a host individual or population.
Inorganic chemicals: Any chemical compound that does not contain one or more carbon atoms. It is noteworthy that plants absorb all their nutrients as inorganic chemicals (e.g., nitrates, phosphates, potash) while the higher animals, and people, absorb all their nutrients as organic chemicals. The exception is iron; plants absorb it in organic form while animals absorb it in inorganic form. Animals also absorb water, oxygen, and common salt as inorganic chemicals.
Insect cages: Small cages, usually constructed of stiff wire covered in muslin or mosquito netting, and used to cover an individual plant in order to confine insects to that plant. The main use for insect cages in plant breeding is to multiply insects for purposes of inoculating a screening population. Alternatively, insect cages may be used to protect research plants from natural infestation, or to measure the population growth rate of an insect, as an indication of host resistance to that insect.
Insect culture: The multiplication of insects, usually in insect cages, for purposes of inoculating a screening population. This inoculation might involve screening for horizontal resistance to the insect in question, or for horizontal resistance to a virus disease of which the insect in question is a virus vector.
Insecticide: A pesticide that kills insects. An insecticide may provide a stable protection (e.g., natural pyrethrins, rotenone, nicotine, soap, oils, etc.) in which case it does not break down to new insecticide-resistant strains of the insect. Or it may provide an unstable protection (e.g., DDT, and most modern synthetic insecticides) and lead to a boom and bust cycle of insecticide production.
Insects: Insects are a Class of Arthropods that have three pairs of legs, and three body regions (head, thorax, and abdomen). In addition, they nearly always have a pair of antennae, and the adults often have one or two pairs of wings. Insects usually reproduce with eggs, but live birth also occurs (e.g., aphids). Insect growth involves a series of 4-8 moults, and the stages between moults are called instars. There is often a metamorphosis, usually at the time of the last instar (e.g., caterpillars turning into butterflies or moths). Most insect parasites of crops cause damage during the early instars, and the function of the final adult instar is often one of reproduction only, without any feeding. See also: Aphid, Beetle, Ladybird, Stem borer, Thrips, Whitefly.
Instar: A stage of growth of an insect that is concluded by the moulting or shedding of the exoskeleton, which is incapable of growth or expansion. Most insect species have 4-8 instars, often concluding with a metamorphosis.
Institutional plant breeding: Plant breeding conducted by a large institute. This kind of breeding is usually expensive and, consequently, it favours cultivars with a wide climatic adaptability. In practice, this means the use of vertical resistance if at all possible. Institutional breeding does not normally allow for farmer-participation schemes and it tends to be autocratic. See also: Corporate plant breeding, Democratic plant breeding, and Self-organising crop improvement.
Integrated pest management (IPM): A system of pest management in which every important parasite in a crop is monitored and crop protection chemicals are used only when absolutely necessary. The idea is to minimise the use of crop protection chemicals in order to reduce biological anarchy and to stimulate biological control. IPM is used mainly against the insect parasites of crops, and it is greatly assisted by horizontal resistance.
Intellectual property protection: Legislation that provides the equivalent of a copyright on a breeder’s registered cultivar. The sale of all propagating material of that cultivar is then controlled, and the breeder earns royalties on those sales.
Intensive crop: A crop that has high profit margins and which consequently justifies considerable expense in its production. Horticultural crops are intensive crops, while cereals are usually extensive crops.
Inter-generic cross or hybrid: A hybrid between two different genera. Inter-generic hybrids are rare, and are usually difficult to make. Not recommended for amateur breeders.
International Agricultural Bureaux: See: CABI
International Research Centres: Agricultural research centres located in non-industrial countries, and financed by industrial countries through CGIAR. The principle centres working with crops are: Maize and wheat (CIMMYT) in Mexico; rice (IRRI), in the Philippines; potatoes (CIP), in Peru; wet tropical crops (IITA), in Nigeria; dry tropical crops (CIAT), in Colombia; semi-arid areas (ICRISAT), in India; and in arid areas (ICARDA).
Internode: The part of a stem that separates two nodes.
Interplot interference: See: Parasite interference.
Interspecific cross or hybrid: A hybrid between two species within the same genus. This type of plant breeding is not generally recommended for amateur breeders who are hoping to develop new cultivars with high levels of horizontal resistance. But attempts at inter-specific crossing can be fun.
IPC: See: CIP.
IPM: See: Integrated Pest Management.
Ipomea batatas: The sweet potato. This crop originated in tropical South America. It was taken by Polynesians to Fiji and New Zealand, where it is known by its Peruvian name ‘kumara’. The Portuguese took it to Africa and the Far East where it is known by its Caribbean name of ‘batatas’, which is the origin of the English word ‘potato’. And the Spanish took it from Acapulco to the Philippines where it is known by its Mexican name of ‘camote’. It is now one of the more important tropical food crops. Although it is cultivated as clones, the crop sets true seed freely, and farmers often keep self-sown seedlings as new cultivar. The harvestable product is a tuber which, in the USA, is often incorrectly called a yam. This is an excellent crop for farmer-participation schemes, and for amateur breeders.; The wild progenitors of sweet potato are extinct. Ipomea purpurea is the morning glory.
Irish famine: See: Hungry forties.
Iron: Iron is an important plant nutrient. It is a component of many enzymes. Iron is also an immobile nutrient and iron deficiency shows first in the young leaves which become pale green and then yellow, even necrotic, but the veins tend to remain green.
IRRI: The International Rice Research Institute, located at Los Baños, Philippines. This is one of the CGIAR research stations.
Irrigation: The process of supplying a crop with water. Irrigation may be overhead irrigation with sprinklers, or furrow irrigation with water poured between the rows. Flood irrigation is used with rice paddies, and with the annual floods of a river such as the Nile. In areas where water is scarce, drip irrigation and subsurface irrigation are now used.
Isatis tinctora: This plant provides a natural blue dye called woad, which is inferior to indigo.
Isolate: This word can be either a noun or a verb. The noun usually refers to a micro-organism that has been obtained as a pure culture from a mixture of organisms. The verb refers to the process of making an isolate.
Isolation from foreign pollen: When subjecting an open-pollinated crop to recurrent mass selection, it must be isolated from other compatible crops to ensure that no unwanted pollen from outside introduces unwanted characteristics, such as susceptibility, in the population breeding.
Isolation to protect neighbours: Plant breeders may choose to isolate their work, in either time or space, or both, in order to protect neighbours from crop parasites. For example, the screening plots might be located in the middle of a large field or farm growing a different species of crop. In general, however, the requirements of on-site screening restrict the possibilities of isolation in both time and space.

Glossary: J-K

Jawa: See: Sorghum bicolor.
Jerusalem artichokes: See: Helianthus tuberosus.
Job’s tears: See: Coix lachryma-jobi.
Jola: See: Sorghum bicolor.
Juglans regia: Walnut. Cultivars are propagated vegetatively as clones and it is advisable to grow a mixture of clones to improve pollination.
Jute: See: Corchorus spp.
Jute, bimli: See: Hibiscus cannabis.
Kale: See: Brassica oleracea.
Kaoliang: See: Sorghum bicolor.
Kapoc: See: Ceiba pentandra.
Kenaf: See: Hibiscus cannabis.
Koch’s postulates: Three postulates for demonstrating the pathogenic nature of a micro-organism, which must (1) be isolated from the diseased tissue and cultured, (2) be inoculated into a healthy host and shown to cause the same disease, and (3) be isolated from the inoculated host and shown to be the same organism. These postulates were very important in the late nineteenth century when the pathogenic nature of micro-organisms was still being disputed. But they are not necessary for amateur breeders.
Kohlrabi: See: Brassica oleracea.
Kola: See: Cola spp.
Koracan: See: Eleusine coracana.
K-strategist: For any species, the carrying capacity of the environment is a constant, and it is represented by the letter ‘K’. K-strategists are species in which the population size is more or less constant, and is limited by the carrying capacity of the environment. K‑strategists tend to have large individuals that live for a long time, and which replace themselves by reproducing relatively infrequently with large and biologically expensive offspring (i.e., low birth rates and high survival rates). Elephants and Californian redwoods are K-strategist species. Note that there is a spectrum of continuous variation between the extreme K‑strategist and its converse, the extreme r‑strategist.
Kumara: See: Ipomea batatas.

Glossary: L

Labelling: A feature of pedigree breeding is that every cross-pollination must be labelled, and this is very labour-intensive. With population breeding, labelling is unnecessary and this labour-saving can be devoted to more useful activities, such as the screening of larger numbers of crosses.
Labiate: A member of the botanical family Labiateae.
Lablab bean: See: Lablab niger.
Lablab niger: The bovanist bean, Egyptian bean, Indian bean, etc. This is a suitable crop for amateur breeders in warm countries working with recurrent mass selection and horizontal resistance.
Laboratory screening: When conducting recurrent mass selection, a laboratory screening can often enhance a field screening by determining aspects of quality that are not discernible in the field.
Labour-saving: Any plant breeding has a limit to the number of person-hours that can be devoted to it. Consequently, any labour-saving device will permit an increase in the number of crosses, and the number of plants in the screening population. When doing recurrent mass selection, there is no need to label crosses, or individual plants, or to keep detailed records of parasitism, etc. The only thing that matters is that the final selections must be the best plants of that generation and, the larger the screening population, the greater the genetic advance. Labour-saving is not laziness. It is increased productivity.
Lactuca sativa: Lettuce. This crop is a member of the Compositae family, and it is the main component of salads. There are four basic types known as ‘crisphead’, ‘butterhead’, ‘romaine’, and ‘leaf’. All types show great variation and there is considerable scope for increased horizontal resistance. The chief disease is downy mildew caused by the fungus Bremia lactucae. Past resistance breeding has involved vertical resistance, and there is scope for horizontal resistance breeding by amateurs.
Ladybirds: Beetles of the family Coccinellidae. These beetles are distinctively oval, almost hemispherical, with a flat under-surface, and they are coloured red or orange, with conspicuous black spots. Both the adults and the larvae of many species of ladybird feed on other insects, particularly aphids, which are crop parasites, and the ladybirds are valuable agents of biological control.
Lagenaria siceraria: The bottle gourd. A monoecious member of the Cucurbitaceae, this is a very ancient crop that pre-dates pottery in many tropical areas. It is apparently the only crop that was common to both the Old World and New World before the development of trans-oceanic travel. Gourds are believed to have originated in Africa, and to have floated across the Atlantic Ocean to Brazil at a very early date. They also spread to India and China, and all parts of S.E. Asia. The dried hard shells of the fruit have a wide range of uses including bottles, bowls, spoons, ladles, tobacco pipes, musical instruments, and floats for fishing nets. The crop has a limited scope for local amateur breeders.
Landrace: A cultivated plant population which is genetically diverse and genetically flexible. A landrace can respond to selection pressures during cultivation. The maize crops of tropical Africa, which were so vulnerable to tropical rust, were landraces, and they responded to the selection pressure for resistance. Prior to the discovery of Johansen's pure lines in 1905, most crop varieties in the industrial world were landraces, and most subsistence crops in the non-industrial world are still landraces. See also: cultivar, Ecotype, Micro-evolution.
Larch: See: Larix spp.
Larix spp.: Larch, which is used as a plantation forest species of softwood. Not recommended for amateur breeders.
Larvae: The early instars of an insect are generally called larvae (singular, larva), particularly in insects that exhibit metamorphosis. Thus caterpillars are the larvae of butterflies and moths. It is often these juvenile stages that are voracious feeders, and that constitute some of the most serious insect parasites of crops. This term should not be confused with the molten rock that comes out of volcanoes, and is spelled lava. See also: Grub.
Late selection: Traditionally, selection is conducted on highly heterozygous individuals which then become the parents of the next screening generation. This is now called early selection. Late selection involves self-pollinating the variable progeny of a cross for 3-4 generations, using either the bulk breeding method or single seed descent, and producing a mixed population of relatively homozygous individuals. The late selection is made among these homozygous individuals.; Late selection is efficient because it produces plants with a reduced hybrid vigour, which can be misleading during the screening process, and it also produces a greater expression of recessive alleles, which are exhibited only in the homozygous state. The features of late selected plants thus have a higher heritability than those of early selected plants. However, this advantage must be equated with the longer breeding cycle required by late selection.
Latent period: In plant pathology, the period between infection and the start of pathogen reproduction. One of the many mechanisms of horizontal resistance is to increase the latent period, thus reducing the reproductive rate of the pathogen.
Lead: Before the days of DDT and synthetic insecticides, highly dangerous compounds of lead were often used to kill crop pests.
Leaf: The main site of photosynthesis, leaves are thin laminae of green tissue, and are typically carried by a stem-like petiole that emerges from a node of the stem. There is usually a leaf bud in the axil of each leaf.
Leaf hopper: Insects of the family Cicadellidae. Many are serious pests of crop plants.
Leaf miner: A plant parasitic insect that mines a tunnel between the upper and lower surfaces of a leaf. The tunnel has a white, translucent appearance, and it starts quite narrow but broadens as the insect larva increases in size.
Leaf spot: A spot, usually irregularly circular, and usually necrotic, caused by a pathogen.
Leek: See: Allium ampeloprasum.
Legume: A cultivated member of the botanical family Leguminoseae.
Leguminoseae: Legumes which are cultivated for their seeds, such as peas, beans, lentils, peanuts, soybeans, and grams, are known as grain legumes or pulses. Those that are cultivated for grazing, or hay, in order to feed farm animals are known as fodder legumes, and include clovers, alfalfa (lucerne), vetches, sainfoin, etc. Most of the pulses are self-pollinating, while the fodder legumes are mainly cross-pollinating.
Lemon: See: Citrus limon.
Lens esculenta: The lentil. A self-pollinated member of the family Leguminoseae, this is one of the oldest pulses and it has been cultivated in the wheat and barley lands of the Old World since the beginnings of agriculture. Most