You are here

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 alloinfecting.
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 alloinfecting 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.