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.