Gossypium barbadense (PROTA)

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Plant Resources of Tropical Africa
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Gossypium barbadense L.


Protologue: Sp. pl. 2: 693 (1753).
Family: Malvaceae
Chromosome number: 2n = 52

Synonyms

  • Gossypium vitifolium Lam. (1786),
  • Gossypium peruvianum Cav. (1788),
  • Gossypium acuminatum Roxb. ex G.Don (1831),
  • Gossypium brasiliense Macfad. (1837).

Vernacular names

  • Cotton, sea island cotton, Egyptian cotton, pima cotton (En).
  • Coton, cotonnier, cotonnier d’Egypte, coton des Indes occidentales (Fr).
  • Algodoeiro, algodoeiro americano (Po).
  • Pamba (Sw).

Origin and geographic distribution

Gossypium barbadense probably originated in Peru as a cross between Gossypium herbaceum L. and Gossypium raimondii Ulbrich or Gossypium gossypioides (Ulbrich) Standley. It grows naturally on the coasts of Peru and Ecuador. It was domesticated in north-western South America. In Peru cotton products from Gossypium barbadense such as yarn, cordage and fishing nets date back to about 2500 BC. Cultivation spread over South and Central America and Gossypium barbadense has been introduced after 1492 into Africa, Asia and the Pacific Islands. It was introduced into the United States in 1785 where it was known as ‘sea island cotton’, as opposed to ‘upland cotton’ (Gossypium hirsutum L.). It is now widely cultivated in the warmer parts of the world and sometimes naturalized. It is the main cotton in Egypt and the West Indies, while other major producers include Sudan, Peru and the United States. In some parts of tropical Africa, e.g. in Côte d’Ivoire, it has to a large extent been replaced by the more productive Gossypium hirsutum.

In this article the word ‘cotton’ refers to information referring to all 4 cultivated Gossypium species (Gossypium arboreum L., Gossypium barbadense, Gossypium herbaceum and Gossypium hirsutum); where information refers to Gossypium barbadense only, this is stated explicitly.

Uses

Cotton is the most important group of fibre plants in the world. The main fibres of cotton plants are the longer seed hairs (‘lint’), used for making yarn to be woven into textile fabrics, alone or in combination with other plant, animal or synthetic fibres. Cotton lint is also made into other products including sewing thread, cordage and fishing nets. The lint of Gossypium barbadense is especially valued for use in high-quality textiles, luxury fabrics, yarns and sewing thread. Cotton textile cuttings and rags serve in the paper industry for the production of the best writing, book and drawing paper. Short fibres (‘fuzz’ or ‘linters’) are processed into a range of products, including papers, twine, automobile upholstery, explosives, plastics and photographic film. Linter pulp is made into various types of paper, depending on its grade. Linters have also been used for the production of cellulose acetate and viscose. Cotton stalks are processed into paper and paperboard, for instance in China, and into cement-bonded particle board.

Cotton is an important oil plant. Oil obtained from cotton seed is industrially used in a range of products, including margarine, mayonnaise, salad and cooking oils, salad dressing and shortening. It is also made into soap, cosmetics, lubricants, sulphonated oils and protective coatings. Locally it serves for cooking and frying. Blends of cotton-oil biodiesel and diesel fuel can be used in conventional diesel engines without any major changes. The seed cake remaining after oil extraction is an important protein concentrate for livestock. Low-grade cake is used as manure. The whole seed can be fed to ruminants, which are less sensitive to the toxic gossypol in the seed than non-ruminants, or is applied as manure. Hulls are a low-grade roughage for livestock or serve as bedding or fuel. Leftover bolls, leaves and thin twigs are grazed by ruminants. Dry stalks serve as household fuel.

In West Africa the fibre of Gossypium barbadense is locally used for weaving articles such as waistbands, neckerchiefs and armlets. In southern Nigeria it forms the basis of a local spinning and weaving industry of some importance. In Cameroon the fibre is made into cloth used for dowries and in burials. In Gabon the fibre is made into bags. In DR Congo it is used for making coarse textiles, cords, string, fishing nets and straps. Gossypium barbadense is sometimes grown as an ornamental. It is a bee forage, giving higher honey yields than Gossypium hirsutum.

Gossypium barbadense is widely used in African traditional medicine. In Senegal a leaf infusion is used as an eyewash for the treatment of eye affections. In Côte d’Ivoire dampened fibre is used as a wound dressing, and fibre soaked in oil is used for drawing. In Mali the leaf juice diluted with water is used as eye drops for the treatment of conjunctivitis. In Benin the leaf juice is taken for the treatment of cough, dystocia and vertigo, and a decoction of the leaves with those of Pergularia daemia (Forssk.) Chiov. is taken against convulsions. In Cameroon a leaf decoction is taken for the treatment of jaundice, pounded leaves are used in poultices against stomach-ache and constipation, and seed oil is used against otitis. In Gabon a leaf maceration is taken against gonorrhoea and as an emetic, while the sap is considered emollient and externally applied against itch. In Congo the leaf sap is instilled in the ear for the treatment of otitis, leaf decoctions are drunk against cough, and the leaf is rubbed on the body to cure scabies. In DR Congo a leaf infusion is drunk for the treatment of colds, bronchitis, rheumatism and haemorrhoids, and kept in the mouth to treat dental caries and gingivitis. Pounded leaves are applied on cuts, abscesses and used for the treatment of leprosy. Pulped young shoots are used against palpitations, and the fibre in dressings on wounds. In Kenya the lint is used as dressing on sores.

Production and international trade

According to FAO estimates the annual world cotton production in 2004–2008 was about 70 million t seed cotton (unginned cotton, containing seed, lint and fuzz), but the largest part (more than 90%) of the world cotton production comes from Gossypium hirsutum. Most of the remainder comes from Gossypium barbadense, which produces longer, stronger, finer and more expensive fibre than Gossypium hirsutum but yields less and shows limited adaptation to most cotton-growing areas. In 2004 the main producers of Gossypium barbadense were the United States, China, India and Egypt. In West Africa commercial production of Gossypium barbadense fibre takes place in Togo and Nigeria. Two other cotton species, Gossypium arboreum and Gossypium herbaceum, are grown to some extent in Africa and Asia.

Properties

Cotton fibres are unicellular extensions of epidermis cells of the seed. Two types of fibres are distinguished: long fibres (‘lint’) and short fibres (‘fuzz’ or ‘linters’). Cotton lint fibres are 10–40(–64) mm long, with a diameter of (12–)18–28(–42) μm and a length:width ratio of 1000–4000. Gossypium barbadense yields the highest quality lint of all cottons, being white, silky and 30–40(–64) mm long. In international trade, the fibre length or ‘staple length’ of cotton is expressed in fractions of inches. Fuzz fibres are similar in appearance to lint fibres, but shorter (2–7 mm long), more cylindrical and with thicker walls. Seeds of some modern Gossypium barbadense cultivars do not produce any fuzz.

Apart from fibre length and its uniformity, the most important properties of cotton are fineness (diameter), maturity, strength and elasticity. The combined fineness and maturity (the degree to which the secondary cell wall has developed) of cotton fibre is usually determined by resistance to air flow, and expressed in a value called ‘micronaire’, reflecting the linear density of fibres. Typical values of the tensile strength, elongation at break, and Young’s modulus of cotton fibre are 285–595 N/mm², 7.0–8.0% and 5500–12,600 N/mm², respectively. Among the world’s major textile fibres, cotton has a unique combination of properties, being strong, comfortable, washable, durable and printable. It also blends well with other fibres to give it additional strength, lustre and crease resistance. On a dry weight basis, cotton fibre contains 88–96% α-cellulose, 3–6% hemicelluloses and 1–2% lignin.

Cotton seeds remaining after ginning consist of linters (5–10%), oil (15–33%), oilcake (33–45%) and hulls (24–34%). Cottonseed oil is a semi-drying oil obtained by mechanical and/or solvent oil extraction from the seed. The principal fatty acids in cottonseed oil are linoleic acid (42–59%), palmitic acid (20–34%) and oleic acid (13–25%). The seed oil also contains 0.5–1(–2)% cyclopropenoid fatty acids, which are known to cause physiological disorders in animals. The oil as well as other plant parts of Gossypium species contain gossypol, a triterpenoid aldehyde, which is toxic to humans and animals, monogastric animals in particular. Gossypol has insecticidal, antimicrobial, antifertility and antitumour properties. Gossypol and related compounds have been implicated in conferring insect tolerance or resistance and antimicrobial properties to cotton plants. Glandless, gossypol-free cultivars exist, but they are more vulnerable to pests. The gossypol content of Gossypium barbadense seeds (0.60–1.15% of total dry matter) is generally higher than that of Gossypium hirsutum (0.51–0.77%), with a higher proportion of the gossypol present in the more biologically active free form. Gossypol can be removed from the oil by solvent extraction, following mechanical and/or solvent oil extraction from the seed. The cake and meal contain over 40% crude protein, but are not without danger for monogastric animals, because of the gossypol they contain. The gossypol in the cake can be removed or made harmless by chemical (ferrous salts) or physical (heating) means, but this is more difficult to achieve economically than removing gossypol from the oil.

When whole seeds are fed to cows, the fuzz on the seeds slows down the passage of the seed through the digestive tract, and fuzz-free Gossypium barbadense seeds are not as completely digested as fuzzy seeds. To increase their digestibility they are cracked or processed. It has been suggested that adult cattle should have less than 0.1–0.2% gossypol in the total ration, which would amount to 2.7–3.6 kg of unprocessed Gossypium barbadense seed per day.

A crude leaf extract of Gossypium barbadense and its methanol fraction showed in-vivo hypotensive effect in rats.

Adulterations and substitutes

The fibre of Gossypium barbadense can be substituted by that of Gossypium hirsutum and the less important Gossypium arboreum and Gossypium herbaceum, but fibre of the latter three species is shorter and of lower quality than that of Gossypium barbadense.

Description

Perennial shrub or annual subshrub up to 3 m tall, with nearly all parts irregularly dotted with black oil glands; twigs first angled, later terete, often tinged with purple. Leaves spirally arranged; stipules linear, lanceolate or ovate, in flowering shoots often broadly ovate to orbicular and auricled at base, 1–5 cm long; petiole ½–? the length of the blade; blade orbicular to broadly ovate in outline, 8–20 cm in diameter, 3–7-palmately lobed with central segment largest, upper leaves sometimes not segmented, lobes ovate to lanceolate, base cordate, margin entire, pedately 3–9-veined, with 1–3 central veins with an elliptical nectary slightly above the base beneath. Flowers solitary, usually on sympodial branches; pedicel shorter than petiole, not articulated, sharply trigonous, usually bearing nectaries below the insertion of the epicalyx segments; epicalyx segments (bracteoles) 3, erect, appressed against corolla or fruit, orbicular to ovate, 4–6 cm long, at base cordate and strongly auricled, with 5–17 acuminate teeth, persistent; calyx cupular, 8–10 mm long, with 5 obtuse short teeth at truncate apex, densely gland-dotted, bearing 3 nectaries outside at the base, splitting after flowering; corolla usually yellow with a dark red or purple spot at the base, petals 5, imbricate, obovate, 5–8 cm long, truncate and emarginate at apex; stamens numerous, forming an erect column 2.5–4 cm long, filaments short, anthers 1-celled; pistil with 3–5-celled ovary and one short style with clavate, 3–5-sulcate stigma. Fruit (‘boll’) an ovoid to fusiform capsule 3.5–6 cm long, beaked, glabrous, densely pitted, black, opening loculicidally, 3-celled with several seeds per cell. Seeds ovoid, 8–10 mm long, with an acute hilum, black to dark brown, with a dense covering of long, fine, white woolly hairs (lint or floss) and a fine, short tomentum (fuzz) everywhere or only at the hilum or absent. Seedling with epigeal germination.

Other botanical information

Gossypium comprises about 50 species distributed in warm temperate to tropical zones. The origin of the genus is unknown, but 3 primary centres of diversity exist: in Australia, in north-eastern Africa to Arabia, and in western-central to southern Mexico. The 4 cultivated cottons of the world (the Old World diploids Gossypium arboreum and Gossypium herbaceum and the New World tetraploids Gossypium barbadense and Gossypium hirsutum) have been domesticated independently in different parts of the world. The taxonomy of Gossypium is complicated, partly due to the domestication of 4 distinct species and extensive interspecific hybridization. The literature is confusing and authors disagree on the identity of many species, subspecies, sections, varieties, forms, races and cultivars that have been distinguished. Currently the taxonomic system of P.A. Fryxell, with about 50 species grouped into 4 subgenera and 8 sections, is the most generally accepted one. It is mainly based on morphological and geographical data, but is confirmed by cytogenetic and molecular evidence. Cytological research has led to the recognition of 8 basic diploid ‘genomic groups’, designated A through G, plus K. In general, species within a genomic group can form fertile interspecific hybrids. Gossypium barbadense and Gossypium hirsutum belong to subgenus Karpas: tetraploid New World species with AD-genome, whereas Gossypium arboreum and Gossypium herbaceum are included in subgenus Gossypium: diploid Old World species with A-genome.

Within Gossypium barbadense 2 varieties are distinguished:

– var. barbadense: annual shrub, cultivated mainly in the West Indies, Central America and the southern parts of the United States, but also in Egypt and Sudan.

– var. braziliense (Raf.) Fryxell: the ‘kidney cottons’ of the Amazon Basin, with the seeds in each cell of the fruit fused into a solid kidney-shaped mass; the kidney seed mass facilitates hand ginning; it is perhaps better considered a geographically restricted domesticated form of Gossypium barbadense than a taxonomic entity.

Formerly, a third variety was distinguished, var. darwinii (Watt) J.B.Hutchinson, but it has been reclassified as a separate species, Gossypium darwinii Watt: a perennial shrub with fine brown lint, endemic to the Galapagos Islands. This separation is supported by evidence from molecular data.

Anatomy

Cotton lint fibres are smooth-looking, ribbon-like and twisted, with the fibre walls showing longitudinal and spiral striations. The fibre walls contain many layers of cellulose chains, which run spirally and give dry fibres their characteristic twisting appearance. The hairs are covered with a waxy cuticle, giving unprocessed fibre a greasy feel and making it water-repellent. On drying at maturity the fibres lose their tubular shape and become ribbon-like (kidney-shaped in cross-section), twisting in different directions forming the well-known convolutions. Desiccation at maturity is an irreversible physical process, generating technological properties that make the cotton fibre very suitable for textile production.

Growth and development

Cotton is normally a perennial plant with an indeterminate growth habit, but is usually grown as an annual, with the formation of nodes on the main stem stopped by fruit load, temperature, soil moisture, photoperiod, or a combination of these factors. The crop cycle is 120–220 days. Seedlings emerge 5–15(–30) days after sowing and the first true leaf unfolds 7–9 days later, but these processes vary with temperature. Upon germination, seedlings initiate a long taproot, which can reach a depth of more than 25 cm by the time the cotyledons unfold and may reach a depth of 3 m by mid-season. The plant remains unbranched for about 1 month. The shoot system is dimorphic, with the main axis and lower branches (emerging from axillary buds) being monopodial and vegetative, whereas the fruiting branches (emerging from extra-axillary buds) are sympodial. Fruiting branches develop as primary branches higher on the main stem and as secondary branches on vegetative branches. Generally only one fruiting branch develops at each node, with 3–5 fruits per branch. In Gossypium barbadense the first fruiting branch appears at node 10–12 of the main stem, and 50–65 days after emergence the first visible flower buds appear as small, green, pyramidal structures, known as ‘squares’. Cotton flowers mostly open near dawn and pollination normally occurs within a few hours. Self-pollination is the predominant mating system, but visiting insects can cause considerable outcrossing (up to 40%). The flowers turn pink in the afternoon and red by the following day. They start withering late on the second day and die on the third day. Flowering peaks at 3(–6) weeks after the onset and may continue for about 6 weeks. The fruits grow very quickly after pollination, reaching their final size in 15–25 days. After a further (20–)25–45(–60) days, depending on genotype and environmental conditions, they are ripe. Usually the dry fruits open at their sutures and the white, fluffy fibre-mass emerges. The seeds remain attached to the placenta and are only separated by picking or by very strong rain or wind.

During the first 2–4 weeks after flowering (the elongation phase) the fibres grow rapidly, reaching their full length, and during the next 4–6 weeks (the secondary thickening phase) the cell walls of the fibres thicken through deposition of cellulose in consecutive layers. The cell wall thickness of a fibre, or the degree to which the fibre has been filled with cellulose, mainly depends on plant vigour during ripening. Upon boll opening the fibre dries and the lumen collapses, resulting in the characteristic twisted, ribbon-like appearance of the fibre that makes it spinnable.

Shedding of squares and young bolls is common in cotton. It is aggravated by adverse conditions such as prolonged overcast weather, extreme temperatures, water stress, waterlogging, nutrient deficiencies, diseases and insect damage. Commonly 60% of the squares and young bolls are shed, but flowers are rarely shed. The ability to overcome adverse events by compensatory growth is characteristic for cotton. However, recovery is only partial and insignificant when severe insect damage occurs late in the season.

Ecology

Gossypium barbadense requires a temperature of (15–)22–32(–38)°C and a rainfall of (500–)750–1250(–1500) mm during the growing season. It is able to germinate at lower temperatures than Gossypium hirsutum. A dry period is needed for fruit ripening. Gossypium barbadense is sensitive to frost and does not tolerate shading. It can be grown on medium to deep, light to heavy, well-drained soils with a moderate fertility and a pH of (5.0–)5.2–7.2(–8.5). In Central Africa Gossypium barbadense is naturalised in savanna, abandoned villages, around houses and along rivers; in Rwanda and Burundi it occurs up to 1650 m altitude. In East Africa it occurs from sea-level up to 1200 m altitude in gardens and experimental plots and as an escape.

Propagation and planting

Cotton is propagated by seed. Seed saved from the previous harvest is rarely used, as the entire harvest is usually sold for ginning. Organized seed multiplication and distribution is important to guarantee seed quality and purity. It is usually recommended that seed be delinted by mechanical or chemical means, with the former being preferred for economic and environmental reasons. For mechanical sowing, removal of the fuzz is essential. Seeds lose their viability rapidly if their moisture content exceeds 10%, but seeds with a moisture content of 7% can be stored in sealed jars for up to 15 years. The 1000-seed weight of Gossypium barbadense is 50–100 g.

Cotton is sown directly in the field, and in tropical Africa this is generally done by hand. The sowing date is chosen in such a way that the harvest will coincide with the beginning of the dry season. The planting density varies widely with cultivar, climate and soil characteristics, and cultivation as well as harvest methods. Spacings are 50–120 cm between rows and 15–60 cm within the row. It is advised not to sow less than 5 seeds per hill. About 20–25 kg/ha delinted seed is necessary for sowing, for instance at 80 cm × 30 cm spacing (41,700 hills/ha) with 5 seeds per hill. The seed should not be sown deeper than 4–5 cm in sandy soils and 2–3 cm in clay soils. Fuzzy seeds require more water for germination compared to delinted seeds because imbibition of water is faster in delinted seeds.

Good soil preparation before sowing is very important, because the seedlings do not penetrate hard or crusted soils easily and do not compete well with weeds until they are 3 weeks old. Dry season weeds can be killed by harrowing or hoeing. This greatly reduces weed competition after planting. Early soil cultivation, allowing early planting, extends the growing season. Although hand hoeing is predominant in some parts of Africa, animal- and tractor-drawn ploughs are being used more and more. Most cotton in Africa is grown on the flat, but ridges are necessary on poorly drained soils.

It is possible to propagate cotton vegetatively by cuttings, budding or grafting. In experiments with Gossypium barbadense it was found that the rooting ability of cuttings decreased with increasing age of the parent plant from 6 (100% rooting) to 18 weeks (10% rooting). Good results were obtained with cuttings with several internodes, taken from the monopodial, vegetative branches and from the upper half of the main shoot (with the apex removed), but cuttings from generative branches did not form roots. The development of rapid, reproducible and genotype-independent systems of in-vitro propagation of Gossypium species has been difficult, though methods have now been developed to produce large numbers of somatic embryos from callus from hypocotyl or cotyledon explants of Gossypium arboreum, Gossypium barbadense, Gossypium herbaceum and Gossypium hirsutum.

Cotton is usually grown in rotation with other crops to control pests and soil-borne diseases. It may be intercropped with other annual crops, such as maize, sorghum and grain legumes. In southern Nigeria Gossypium barbadense is often grown in mixed cropping systems with yams, maize and cowpea. In Cameroon it can be found along paths and in medicinal gardens.

Management

Within 2 weeks after sowing, gaps in the stand of cotton are resown, the crop is thinned and a first weeding round takes place. A second weeding and the final thinning and ridging are carried out 4–5 weeks after sowing, and the final weeding another 2–3 weeks later. In tropical Africa weeding is usually done by hand, but in West Africa draught animals are often used for between-row weeding and ridging. Herbicides are sometimes applied.

Cotton has a very good nutrient uptake ability, and nutrient requirements are therefore moderate. The uptake of a crop producing 1680 kg/ha seed cotton has been estimated at 105 kg N, 18 kg P and 66 kg K per ha. With the seed cotton 40 kg N, 7 kg P and 14 kg K per ha are removed; with the crop residues (especially the leaves) 65 kg N, 11 kg P and 52 kg K per ha are removed. Half the N and all P and K are usually applied around sowing. The second application of N is given about a month after sowing, at final thinning. Too much N stimulates vegetative growth and extends the vegetative period, whereas N-shortage leads to chlorosis, reduced growth and boll-shedding. Gossypium barbadense is more sensitive to excess N than Gossypium hirsutum. Sufficient K is important for cotton fibre quality and disease resistance and shortage leads to mottled yellowish leaves with brown concentric spots, with the leaf margins drying and curling inwards, and the leaves eventually drying out and being shed. P-deficiency results in dark green leaves and delayed flowering and fruiting.

Gossypium barbadense is more often grown with irrigation than Gossypium hirsutum. Under rainfed conditions supplemental irrigation may help early planting and alleviate dry spells in mid season. To stop vegetative development, irrigation should cease shortly after boll opening has started.

Cotton can be grown as a perennial and be cut back and ratooned, but this is not advisable, because perennial cotton can act as a host reservoir for cotton pests and diseases.

Diseases and pests

Diseases are less important in cotton than pests. The most widespread diseases are bacterial blight, leaf spot, blackarm or boll rot caused by Xanthomonas axonopodis pv. malvacearum (synonym: Xanthomonas campestris pv. malvacearum), anthracnose caused by Glomerella gossypii (anamorph: Colletotrichum gossypii), Fusarium wilt caused by Fusarium oxysporum, and Verticillium wilt caused by Verticillium dahliae. Bacterial blight is controlled by growing cotton only once every 3 or more years on the same field, removing the harvest remains and seed treatment. Anthracnose can be controlled by the same measures, but resistant cultivars are not available. Gossypium barbadense cultivars with resistance against Fusarium wilt and Verticillium wilt are available. Cropping methods to control wilt diseases include crop rotation, sufficient K-fertilization and the control of nematodes. The most important virus diseases of cotton in tropical Africa are leaf curl, African cotton mosaic and cotton blue disease. Virus diseases are controlled by eliminating reservoir hosts and vectors, and by using tolerant or resistant cultivars.

Cotton suffers from a wide spectrum of pests. Bollworms are among the most serious pests. They feed inside the bolls, damaging lint and seed and so causing considerable reduction in yield and quality. The main bollworms are American bollworm (Helicoverpa armigera), pink bollworm (Pectinophora gossypiella) and spiny bollworm (Earias spp.). Spiny bollworm, to which Gossypium arboreum and Gossypium barbadense seem less susceptible than Gossypium hirsutum, has a serious early effect of tipboring in the main stem leading to excessive formation of vegetative branches and delaying the setting of bolls, which makes them vulnerable to mid-season American bollworm and stainers. Resistance to bollworms has not been achieved to the desired extent, and their control has long relied heavily on insecticides.

Leaf, stem and bud-sucking bugs can cause considerable damage. Jassids (Amrasca, Empoasca, Erythroneura, Jacobiella and Jacobisca spp.) are the first pests to appear, but a dense coating of long hairs on leaves and stems provides good protection. Whitefly (Bemisia tabaci) and cotton aphid (Aphis gossypii) are pests later in the season; the former is the vector of leaf curl and African cotton mosaic, the latter of cotton blue disease. Early sowing, weeding and harvesting and the use of short-season cultivars can reduce their damage. Cotton stainers (Dysdercus spp.) occur in all cotton-growing countries. They pierce the green bolls and inject the fungus Nematospora gossypii, which causes yellow staining of the lint, resulting in lower quality. About 4 alternating sprays of organophosphates and pyrethroids can overcome this pest. Fairly effective preventive control can be obtained by strict phyto-sanitation, early cropping of maize or sorghum followed by early ploughing and close planting of cotton using an early-maturing cultivar. The boll weevil (Anthonomus grandis) is economically the most serious cotton pest in the United States. Close relatives of cotton, such as Abutilon species growing nearby are alternative hosts of cotton pests, especially stainers.

Insect pests in cotton have been effectively controlled since 1945 with the use of insecticides. The repeated development of resistance of insect pests (especially the American bollworm) to new insecticides has in some countries led to excessive spraying, up to 15 sprays per season, killing all natural enemies. This may also induce outbreaks of previously minor pests, requiring additional spraying. To reduce the use of pesticides, the application of Integrated Pest Management (IPM) or Integrated Weed and Pest Management (IWPM) is advocated. Very early field preparation including repeated weeding, fertilizer application, early planting of jassid-resistant cultivars, gapping, thinning and judicious use of pesticides on the basis of insect monitoring and damage thresholds, form the basis of interacting IWPM farming practices. Preventive weed control by ploughing or hoeing promptly after clearing the preceding crop stores moisture from unexpected storms in the subsoil which makes it possible to plant early. This encourages early fruiting well ahead of the main pest, American bollworm, and provides ample time for compensatory fruiting in case of early fruit damage. As insecticides against jassids are no longer needed they do not kill the natural enemies which control American bollworm in its vulnerable young stage. By the time the later pink bollworms, stainers and whitefly occur, the main crop will be safe.

The most widely distributed economically important nematode in cotton is the root-knot nematode (Meloidogyne spp.), whereas the reniform nematode (Rotylenchus spp.) is more restricted to tropical and subtropical environments. Gossypium arboreum, Gossypium herbaceum and Gossypium barbadense are less susceptible to the reniform nematode than Gossypium hirsutum. Nematodes can be controlled by rotation and chemicals, whereas cotton genotypes have been developed with some tolerance to the reniform nematode.

Harvesting

In tropical Africa cotton harvesting is generally done by hand, usually in 3 rounds, because leaving open bolls in the field may result in deterioration of lint quality. The first picking starts about 10 days after the fruits have opened, the other rounds follow at intervals of a little over 1 week. The cotton should be sorted right away during harvesting into white cotton, stained cotton and waste. At harvesting, the cotton must be as dry as possible. In forest regions and in the event of late rains, additional drying on racks may be necessary. Hand-picking gives cleaner cotton and a higher recovery than mechanical harvesting.

Mechanical harvesting is practised in the United States and Australia, where hand-picking is too expensive; here low-growing, weakly-branching cultivars are sown at narrow spacings, and plants are sprayed with defoliants before harvesting. Mechanically harvested fibre needs heating and shaking to remove impurities, and this operation makes the fibre more brittle.

After picking, the seed cotton is cleaned and transported in bags or sheets to the ginnery for checking, weighing, sorting and payment. The seed from the first ? of the crop picked is usually the most viable and may be kept separately in clearly marked bags. The lint from the first ? of the crop is the most mature and strong.

After the cotton has been harvested, the cotton stems should be uprooted and burnt to prevent the build-up of pest and diseases.

Yield

A seed cotton yield of up to 4 t/ha is possible under optimal conditions, but in practice it is seldom over 2.5 t/ha and the average world yield is about 2 t/ha. In most tropical African countries the yield is around 1 t/ha. Seed cotton of primitive cultivars yields 20–25% fibre after ginning, whereas good cultivars of upland cotton have a ‘ginning-outturn’ of at least 35% and sometimes over 40%. The yields of Gossypium barbadense are relatively low, compared to those of Gossypium hirsutum.

Handling after harvest

In most tropical African countries, the harvested cotton is marketed through national agencies, but in some countries (Nigeria, Kenya) it is done in collaboration with the private sector. In the case of national structures, yield forecasts are made by extension workers, to enable the mobilization of sufficient transport and processing facilities. In most countries the harvested cotton is separated into clean seed cotton and stained or trashy seed cotton.

Cotton lint is removed from the seeds by ginning, which can be done with a hand gin (capacity of 2–3 kg lint/hour) or mechanically. Mechanical ginning can be done with a saw gin (capacity of 300 kg lint/hour) for the shorter stapled cottons, or with the more gentle roller gin (capacity of 30 kg lint/hour) for the longer stapled fine types. In some African countries, such as Kenya and Uganda, roller ginning is common, even for shorter stapled cotton. In West and Central Africa manual ginning may be done by placing the seed cotton on a block of wood or a flat stone, and squeezing out the seeds by rolling an iron or wooden rod over it. The optimum moisture content of the fibre for ginning is 5–7%. When the moisture content is lower, excessive fibre damage occurs; when it is higher, the amount of broken seeds is higher. The ginning outturn (the fibre weight as a percentage of the weight of the seed cotton) ranges from 44% in Côte d’Ivoire to 28–35% in DR Congo. After ginning, the fibres are pressed into bales of 216 kg and the seeds are transported to the oil mill.

Cotton fibre quality is defined in terms of its length and uniformity, strength, elasticity and maturity, whereas whiteness and trash content also play a role. These properties can all be measured rapidly by the ‘High Volume Instrument’ (HVI).

At the oil mill, fuzz is removed by additional saw ginning before seeds are crushed. The oil is usually extracted mechanically in a screw press, or chemically with a solvent.

Genetic resources

The Cotton Germplasm Collection of the United States Department of Agriculture, Agricultural Research Service (USDA/ARS) at College Station in Texas, United States, contains about 1600 accessions of Gossypium barbadense. The Brazilian Agricultural Research Corporation (EMBRAPA) maintains the Brazilian collection with about 1500 Gossypium barbadense accessions. In Uzbekistan the Cotton Breeding Institute, the Institute of Genetics and Plant Experimental Biology and the National University of Uzbekistan together hold about 1300 Gossypium barbadense accessions. In Russia the N.I.Vavilov Institute of Plant Industry (VIR) in St Petersburg holds about 1100 accessions of Gossypium barbadense. The cotton collection of the Chinese Academy of Agricultural Sciences (CAAS) kept in Beijing, Anyang and Hainan Island, contains about 600 Gossypium barbadense accessions. In India about 500 Gossypium barbadense accessions are kept at the Central Institute for Cotton Research (CICR) in Nagpur and Coimbatore, and the National Bureau for Plant Genetic Resources (NBPGR) in New Delhi. The genebank of the Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD) at Montpellier, France, also contains about 500 accessions of Gossypium barbadense.

Breeding

Until the 1930s cotton breeding was limited to crossing within the diploid and tetraploid groups. After this, polyploidization of the diploids greatly increased breeding opportunities. Crosses between Old World and New World genotypes have become important, especially for resistance breeding and the breeding of better cultivars for regions in Asia where Gossypium arboreum and Gossypium herbaceum grow well, but Gossypium hirsutum does not. F1 hybrid cultivars with considerable hybrid vigour for yield have been successfully developed. However, the available systems of cytoplasmic male sterility have been inadequate for large-scale production of hybrid seed, mainly due to incomplete expression of fertility restorer genes in the male parents. Current use of cotton hybrids is limited to South Asia and China, where seed production by manual emasculation and pollination is economically feasible because of low labour costs.

The main objectives in cotton breeding, apart from higher yields, are photoperiod-insensitivity, early maturity, adaptation to mechanical harvesting (through low growth, little branching, short flowering period, loosely attached seeds, less hairy leaves), fibre quality (length, fineness, strength and elasticity), seed quality (high oil content and low gossypol content, increased suitability of the presscake as a source of protein for humans and animals), resistance to diseases (e.g. bacterial blight and Fusarium wilt) and pests (e.g. bollworms, jassids) and tolerance to drought, cold and salinity. There has been little progress in breeding for pest resistance (except for resistance to jassids), but much success has been obtained in resistance and tolerance to Fusarium and Verticillium wilts, bacterial blight and nematodes.

Modern Gossypium barbadense cultivars are highly introgressed with Gossypium hirsutum, and most commercial Gossypium barbadense cultivars have 8–12% Gossypium hirsutum DNA.

Prospects

Cotton will remain very important on a worldwide scale, because of its excellent fibre properties and low price. Although Gossypium barbadense yields high-quality fibre (longer and stronger than that of Gossypium hirsutum), the largest part of the world cotton production comes from Gossypium hirsutum, because Gossypium barbadense needs longer to mature than Gossypium hirsutum, gives lower yields and is more sensitive to suboptimal growing conditions. This situation is unlikely to change much, although it must be added that the distinction between the 2 species becomes more and more blurred as a result of natural and artificial hybridization and gene transfer.

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Author(s)

  • G. Todou, Ecole Normale Supérieure, Université de Maroua, B.P. 55, Maroua, Cameroon
  • S. Konsala, Institut Supérieur du Sahel, Université de Maroua, B.P. 46, Maroua, Cameroon

Correct citation of this article

Todou, G. & Konsala, S., 2011. Gossypium barbadense L. [Internet] Record from PROTA4U. Brink, M. & Achigan-Dako, E.G. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>.

Accessed 12 November 2020.