4

1: Pulses

Vigna unguiculata (L.) Walp.

Repertorium botanices systematicae 1: 779 (1843).

LEGUMINOSAE

2n = 22

- cv. group Unguiculata: Dolichos unguiculatus L. (1753), Dolichos sinensis L. (1754), Vigna sinensis (L.) Hassk. (1844), Vigna unguiculata (L.) Walp. ssp. unguiculata (1970);
- cv. group Biflora: Dolichos biflorus L. (1753), Dolichos catjang Burm. f. (1768), Phaseolus cylindricus L. (1754), Vigna catjang (Burm. f.) Walp. (1839), Vigna unguiculata (L.) Walp. ssp. cylindrica (L.) van Eseltine (1931);
- cv. group Sesquipedalis: Dolichos sesquipedalis L. (1763), Vigna sesquipedalis (L.) Fruhw. (1898), Vigna sinensis (L.) Hassk. ssp. sesquipedalis (L.) van Eseltine (1931), Vigna unguiculata (L.) Walp. ssp. sesquipedalis (L.) Verdc. (1970)

- cv. group Unguiculata: (common) cowpea, black-eye bean, southern pea (En). Haricot dolique, niébé (Fr). Indonesia: kacang tunggak. Malaysia: kacang bol, kacang toonggak, kacang merah. The Philippines: batong, kibal, otong. Cambodia: sândaèk kâng sândaèk ângkuy. Laos: thwàx do. Thailand: tua dam. Vietnam: dôu den, dôu trang, dôu tua.
- cv. group Biflora. (Catjang) cowpea, sowpea (En). Dolique (Fr). Indonesia: kacang merah, kacang peudjit, kacang tunggak. Cambodia: sândaèk sâ, sândaèk khmau, sândaèk krâhâm. Laos: thwàx siênx. Thailand: thua khaao, thua rai, po-thoh-saa. Vietnam: dâu ca, dâu trang, dâu do.
- cv. group Sesquipedalis. Yard-long bean, asparagus bean (En). Dolique asperge, haricot kilomètre (Fr). Indonesia: kacang panjang, kacang tolo, kacang belut. Malaysia: kacang panjang, kacang bêlut. The Philippines: sitao, hamtak, banor. Cambodia: sândaèk troeung. Thailand: tua fak yaow, tua phnom. Vietnam: dâu dûa, dâu giai áo.

Vigna unguiculata originated in Africa, though where the crop was first domesticated is uncertain. Two centres of diversity appear to exist for the species, which contains wild and cultivated forms: one in West Africa (for cv. group Unguiculata) and another in India and South-East Asia (for cv. group Biflora and cv. group Sesquipedalis). Common cowpea is widely distributed throughout the tropics and subtropics (30° N-S), especially in Africa. Outside Africa, it is also grown in Asia, especially India, Australia, the Caribbean, the southern United States and the lowland and coastal areas of South and Central America. Catjang cowpea is cultivated mainly in India and Sri Lanka, and, to some degree, in South-East Asia. Yard-long bean is mostly cultivated in India, Bangladesh and South-East Asia, and Oceania, but it has spread widely throughout the tropics as a minor vegetable crop.

- Cv. group Unguiculata. Cultivated for the seeds (shelled green or dried), the pods or leaves that are consumed as green vegetables or for pasture, hay, silage and green manure. In Africa, where they are the preferred food legume, they are consumed in 3 basic forms: (1) cooked together with vegetables, spices and often palm oil, to produce a thick bean soup, which accompanies the staple food (cassava, yams, plantain); (2) decorticated and ground into a flour and mixed with chopped onions and spices and made into cakes that are either deep-fried (akara balls) or (3) steamed (moin-moin). In India, the common cowpea is used mostly as a pulse, either whole or as dhal. Leaves may be boiled, drained, sun-dried and then stored for later use.
- Cv. group Biflora. In India and Sri Lanka, it is grown for seed and as a vegetable. Tender green pods are consumed as green vegetable. Dried seeds are used whole or split. It makes excellent forage. It is used to make hay and is often mixed with maize or sorghum for silage and for green manure.
- Cv. group Sesquipedalis. Yard-long bean is grown for its succulent young pods and sometimes for its leaves as vegetable. Dry seeds are cooked with meat and fish. Green plants are used as fodder or as a green manure.

World-wide production in 1981 was estimated conservatively at 2.27 million t from 7.7 million ha. Cowpeas are grown extensively in 16 African countries, Africa producing two thirds of the total. Nigeria and Niger produce half the world crop. Brazil produces 26 % of the world total. The estimated area in Asia under different forms of the species is 1 million ha concentrated in India (more than 0.5 million ha), Sri Lanka, Burma, Bangladesh, the Philippines, Indonesia, Thailand, Pakistan, Nepal, China and Malaysia. Most production in South-East Asia is as green vegetable and a limited amount as dry seed. Most production is by smallholders.

Mature seeds contain per 100 g edible portion: water 10 g, protein 22 g, fat 1.4 g, carbohydrates 59.1 g, fibre 3.7 g, ash 3.7 g, calcium 104 mg and small amounts of other nutrients. The energy content averages 1420 kJ/100 g. Lysine content is high, making cowpea an excellent improver of protein quality of cereal grains. Seed weight varies between 10 and 25 g/100 seeds. Raw young green pods per 100 g edible portion: water 88.3 g, protein 3.0 g, fat 0.2 g, carbohydrates 7.9 g, fibre 1.6 g, ash 0.6 g. The energy content averages 155 kJ/100 g.

A prostrate, climbing, erect to suberect, nearly glabrous annual, 0.3-4 m long, with well developed root system. Stems more or less square, slightly ribbed, with nodes usually violet. Stipules prominent, ovate, appendaged. Leaves alternate, trifoliolate, with petiole 5-25 cm long; first two leaflets opposite, asymmetrical, top leaflet symmetrical, ovate, sometimes shallowly lobed, (6.5-)7.0-13.5(-19.5) cm x (3.5-)4.0-9.5(-17.0) cm. Inflorescences are axillary racemes with several flowers clustered near the top; peduncle (4-)10-17(-32) cm long; rachis contracted, tuberculate; fertile flowers attached to a tubercle carrying abortive flowers, leaving gland-like tissue after being shed; bracts 1 per flower, early deciduous; pedicel short; bracteoles 2, deciduous, obovate, 3-5 mm long; calyx campanulate, lobes 5-7 mm long; corolla with erect or spreading standard, 2-3 cm long, hood-shaped when older, wings 22 mm x 12 mm, keel boat-shaped, 21 x 12 mm; stamens diadelphous (9 + 1); ovary with 12-21 ovules. Pod pendent or erect to spreading, linear, 10-100 cm long. Seeds variable in size and shape, square to oblong, 5-10 mm x 4-8 mm, variously coloured.

Cowpea seeds can germinate in 3-4 days under favourable soil moisture and temperature (28 °C). Germination is epigeal. Within 5 days, the cotyledons have lost much of their weight and have begun to abscise. Size of the cotyledons has a direct positive influence on the size of the emerging seedling. The maximum leaf area index (3-4) is achieved between flowering and early pod set in most cultivars, when the crop intercepts the maximum solar radiation. Cowpea can show extreme variation in start and finish of the reproductive period. Some cultivars may start flowering 30 days after sowing and be ready for harvest of dry seed 25 days later; others may take more than 90 days to flower, and take 210-240 days to mature. Most flowers are self-pollinated, though a small proportion of outcrossing occurs, especially in humid climates. Most genotypes of cowpea respond to photoperiod as typical quantitative short-day plants but some genotypes are insensitive to a wide range of photoperiods and warmer circumstances can hasten the appearance of flowers in genotypes that are either sensitive or insensitive to photoperiod. The period of anthesis is characterized by profligate loss of flower buds and open flowers, and afterwards of immature fruits. Pod development is rapid and lasts about 19 days.

Within Vigna unguiculata, the cultivated forms are classified as follows.
- Cv. group Unguiculata (sometimes Vigna unguiculata ssp. unguiculata), the common cowpea: spreading, suberect or erect annual, 15-80 cm high; pods 10-30 cm long, pendent (even when young), hard and firm, not inflated when young; seeds usually 6-10 mm long.
- Cv. group Biflora (sometimes Vigna unguiculata ssp. cylindrica (L.) van Eseltine), the catjang cowpea: spreading, suberect or erect annual, 15-80 cm high; pods 7.5-12 cm long, erect or ascending, hard and firm, not inflated when young; seeds usually 3-6 mm long.
- Cv. group Sesquipedalis (sometimes Vigna unguiculata ssp. sesquipedalis (L.) Verdc.), the yard-long bean: climbing annual, 2-4 m high; pods 30-100 cm long, pendent, more or less inflated and flabby when young; seeds usually 8-12 mm long.

Cowpea is a quantitative short-day plant. Local populations of cowpeas grown by farmers in West Africa are well adapted so that they start to flower at the end of the rains at a particular locality. The optimum temperature to grow and develop is 20-35 °C. Cowpea can grow in a wide range of soils and does well on acid soils. Excessive soil moisture reduces growth but drought can be tolerated.

Propagation is by seed. Common cowpea is traditionally grown in Africa intercropped with cereals like pearl millet, sorghum or maize, at wide spacings (total plant population 10 000-20 000 plants/ha). The bulk of production comes from smallholdings. Tillage normally follows the crop with which cowpea is interplanted. Rate of sowing varies with planting method: when sown in rows, 10-40 kg/ha; for broadcasting, 90 kg/ha. Cowpea is grown in many parts of Asia in sole cropping or intercropped with cereals, cotton or sugar-cane, and relay-cropped in standing rice. Cultivation practices differ widely in the region. In southern India, Sri Lanka, the Philippines, Indonesia and Thailand, most of the crop is grown after rice. During this period, rainfall diminishes and later in the season soil moisture is limited. In rain-fed areas of South-East Asia, early-maturing cultivars could be sown in late April-early May, with harvest at the end of June-early July, before rice is transplanted. For catjang cowpea, seed rate is 15-20 kg/ha in sole cropping but lower in intercropping. Yard-long bean is grown on rice bunds or as a backyard crop. It is grown as sole crop or intercropped with maize, sugar-cane or cassava. Near cities, most farmers grow it as a sole crop on a small scale. Seed rates are 25-50 kg/ha. Yard-long bean is established in rows 75-100 cm apart with hill-to-hill spacing of 20-25 cm. Plant population density is 60 000-70 000 plants/ha.

Most cowpea crops are rain-fed, a few are irrigated and others use residual moisture in the soil after harvest of a rice crop. Cowpea is particularly well suited for rice-based cropping systems. Two to three weedings during the first 1.5 months after planting are recommended. Losses due to weeds can be 30-65 %. Parasitic weeds (Striga spp.), generally associated with continuous cropping of cowpea in Africa, may cause damage too. Plants of yard-long bean are staked when 25-30 days old. In most soils, native Rhizobium strains nodulate the plants. Effective cowpea-Rhizobium symbiosis fix more than 150 kg/ha of N and supply 80-90 % of the nitrogen the host plant requires. Inoculation may be advantageous, if the crop has not been grown for many years. In general, no fertilizers are applied. However phosphorus pentoxide at 30 kg/ha often improves performance. A starter of N at 30 kg/ha may also be beneficial. Cowpea is commonly incorporated in crop rotations in semiarid, humid and subhumid environments.

Cowpea suffers from many viral, fungal and bacterial diseases. Serious viral diseases include cowpea yellow mosaic virus, cowpea aphid-borne mosaic virus, cowpea mottle virus and golden mosaic virus. Crop rotation, weeding to remove alternative hosts and resistant cultivars are necessary for integrated control.
Diseases caused by fungi and bacteria are classified according to plant parts or growth stages most adversely affected. Serious stem diseases in Africa include anthracnose (Colletotrichum lindemuthianum); major foliar diseases include bacterial blight (Xanthomonas vignicola), Cercospora leaf-spots and several rusts. Wilt (Fusarium oxysporum) is common in Asia. Sphaceloma scab and brown blotch (Colletotrichum spp.) are serious pod diseases.
The major diseases can be controlled by appropriate cultural practices, the use of resistant cultivars and by integrated management that implies the complementary use of different control methods. The serious mycoplasm disease is phyllody. Cowpea is attacked by many insect pests throughout its geographic range but especially in Africa. The pests include aphids, beanfly, leafhoppers, thrips, podborers, pod-sucking bugs, cowpea curculio and storage weevils. In Africa, insect pests are often responsible for yield losses, sometimes even crop failure. Serious pests in Africa are: aphids (Aphis craccivora), thrips, pod bugs, pod borers (Maruca testulalis) and storage weevils (Callosobruchus spp.). In Asia, serious pests seem to be aphids, leaf hoppers (Empoasca spp.), beanfly (Ophiomyia phaseoli) and storage weevils. Control measures include the use of insect-resistant cultivars in combination with cultural control methods and application of insecticides in minimal amounts. Economic losses also occur from nematodes like root-knot nematodes (Meloidogyne spp.) and reniform nematodes (Rotylenchulus spp.). Control measures include crop rotation, fallow and resistant cultivars.

Green pods are harvested by hand when they are still immature and tender (12-15 days after flowering). Pod picking may continue for 6-8 weeks for yard-long bean. When grown as a pulse, harvesting is complicated by the prolonged and uneven ripening of many cultivars. Time of harvesting is critical as mature pods easily shatter. So they are hand-picked now and then. Sometimes plants are pulled when most of the pods are mature. For hay, the crop is cut when most of the pods are well developed. Harvesting is done by hand or mechanically.

Under subsistance agriculture in Africa, average yield of seed is 100-300 kg/ha. When grown as a sole crop with good management, cowpea can yield 1000-4000 kg/ha. Largest yields have been achieved by crops late to flower and mature. Yields of dry seeds in South-East Asia are usually higher than in West Africa. Yields of catjang cowpea in India are 1000-2500 kg/ha. Yield of green pods of yard-long bean is 6-8 t/ha.

After threshing, seed should be thoroughly dried to a moisture content of 14 % or less before being stored. Cowpeas are extremely susceptible to insect infestation during storage. Farmers may treat seeds with palm, groundnut or coconut oil as protection during storage. Most of the harvest is sold and consumed locally. Considerable amounts of cowpeas are processed in the United States. Yard-long beans may be quick-frozen but since the pods wilt quickly after picking, they must be processed with a minimum of delay in order to achieve an acceptable product that can compete with snap beans (Phaseolus vulgaris).

The most extensive collection of germplasm is maintained at the International Institute of Tropical Agriculture, Ibadan, Nigeria, with 10 000 accessions. However germplasm from South-East Asia is not well represented. There is a need to collect local Asian germplasm and to expand the collections of certain areas of cowpea and wild relatives for successful crop improvement. The collections of the weedy and closely related species of cowpea are limited. The gene pool that can currently be exploited by cowpea breeders comprise the cultivar groups and their landraces as well as all the wild subspecies of Vigna unguiculata.

Insect pests and pathogens are the principal factors limiting productivity throughout Africa, whereas both sensitivity to photoperiod and intermediate plant types are relevant in traditional farming. The strategy of IITA is now to incorporate pest and disease resistance and photoperiodic reactions into a range of plant types, suited to different cropping systems and environments. Breeding for resistance to drought and heat is necessary for the production of cowpeas in semiarid zones. Considerable emphasis is placed on developing extra early cowpea cultivars for areas with short rainy seasons and for areas where a catch crop after rice or wheat is possible (60-90 days). Breeding work on yard-long bean is almost non-existent. The University of the Philippines, Los Baños, developed several cultivars by crossing yard-long bean and common cowpea (so-called bush sitao) for vegetable purpose. To improve the productivity of yard-long bean, breeding for resistance to pests and diseases and improved plant types are required. The cultivated and wild forms of cowpea in southern Africa are promising for improvement programmes.

The prospects for Vigna unguiculata are reasonably good through crop improvement and better management practices. Efforts to gather genetic resources and use in breeding are the keys for future improvement. Cowpea is of great value in multiple cropping systems involving relay cropping and mixed intercropping. It also has great potential as a short-duration catch crop in several Asian countries. As the demand for vegetables will grow in South-East Asia, yard-long bean may play a useful role in supplying proteins and vitamins.

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Kay, D.E., 1979. Food legumes. Tropical Products Institute, London. Crop and Product Digest No 3. p. 11-16, 86-114.
Lush, W.M. & Evans, L.T., 1981. Domestication and improvement of cowpea. Euphytica 30:579-587.
Marechal, R., Mascherpa, J.-M. & Stainier, F., 1978. Etude taxonomique d'une groupe complexe d'especes des genres Phaseolus et Vigna (Papilionaceae) sur la base de donnees morphologiques et polliniques, traitees par l'analyse informatique. Boissiera 28:191-196.
Rawal, K.M., 1975. Natural hybridization among wild, weedy and cultivated Vigna unguiculata (L.) Walp. Euphytica 24:699-707.
Singh, S.R. & Rachie, K.O. (Editors), 1985. Cowpea research, production and utilization. John Wiley & Sons, Chichester, Essex. 460 pp.

R.K. Pandey & E. Westphal

Pandey, R.K. & Westphal, E., 1989. Vigna unguiculata (L.) Walp.. In: van der Maesen, L.J.G. & Somaatmadja, S. (Editors): Plant Resources of South-East Asia No 1: Pulses. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea