Vigna unguiculata (PROSEA Pulses)

Plant Resources of South-East Asia
Introduction

List of species

Vigna unguiculata (L.) Walp.

Protologue: Rep. Bot. Syst. 1: 779 (1842).

Family: Leguminosae

Chromosome number: 2n= 22

Synonyms

Cv.-group Unguiculata:

Dolichos unguiculatus L. (1753),
D. sinensis L. (1754),
Vigna sinensis(L.) Hassk. (1844),
Vigna unguiculata (L.) Walp. ssp. unguiculata (1970).

Cv.-group Biflora:

Dolichos biflorus L. (1753),
D. 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).

Vernacular names

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
Philippines: batong, kibal, otong
Thailand: tua dam
Vietnam: dôu den, dôu trang, dôu tua
Laos: thwàx do
Cambodia: sândaêk kâng, sândaèk ângkuy.

Cv.-group Biflora:

(catjang) cowpea, sowpea (En)
dolique (Fr)
Indonesia: kacang merah, kacang peudjit, kacang tunggak
Thailand: thua khaao, thua rai, po-thoh-saa
Vietnam: dâu ca, dâu trang, dâu do
Laos: thwàx siênx
Cambodia: sândaêk sâ, sândaêk khmau, sândaêk krâhâm.

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
Philippines: sitao, hamtak, banor
Thailand: tua fak yaow, tua phnom
Vietnam: dâu dûa, dâu giai áo
Cambodia: sândaèk troeung.

Origin and geographic distribution

V. unguiculata originated in Africa, although 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 USA and the lowland and coastal areas of South and Central America. Catjang cowpea is mainly cultivated in India, 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.

Uses

Cv.-group Unguiculata: cultivated for the seeds (shelled green or dried), the pods and/or leaves that are consumed as green vegetables or for pasturage, hay, ensilage, and green manure. In Africa, where they are the preferred food legume, they are consumed in 3 basic forms:

cooked together with vegetables, spices and often palm oil, to produce a thick bean soup, which accompanies the staple food (cassava, yams, plantain),
decorticated and ground into a flour and mixed with chopped onions and spices and made into cakes which are either deep fried (akara balls), or
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 for making hay, and, 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.

Production and international trade

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 about 50% of the world crop. Brazil produces 26% of the world total. The estimated area in Asia under different forms of the species is about 1 million ha concentrated in India (more than 0.5 million ha), Sri Lanka, Burma, Bangladesh, Philippines, Indonesia, Thailand, Pakistan, Nepal, China and Malaysia. Most of the production in South-East Asia is as green vegetable and only a limited amount as dry seed. Most of the production is realized by smallholders.

Properties

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 energetic value averages 1420 kJ/100 g. Lysine content is relatively 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 contain 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 energetic value averages 155 kJ/100 g.

Description

A prostrate, climbing, erect to suberect, nearly glabrous annual, 0.3-4 m long, with well-developed root system. Stems ± 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 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 x 12 mm, keel boatshaped, 21 x 12 mm; stamens diadelphous (9 + 1); ovary 12-21- ovulate.
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.

Growth and development

Cowpea seeds can germinate in 3-4 days under favourable soil moisture and temperature (about 28 °C). Germination is epigeal. Within 5 days the cotyledons have lost much of their weight and have begun to abscize. 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 end of the reproduction period. Some cultivars may start flowering within 30 days from sowing and be ready for dry seed harvest 25 days later; others may take more than 90 days to flower and take between 210 and 240 days to mature. Most flowers are self- pollinated, although a small proportion of outcrossing always occurs, especially in humid climates. Most cowpea genotypes 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 both photoperiod-sensitive and insensitive genotypes. The period of anthesis is characterized by profligate loss of flower buds and open flowers and, thereafter, of immature fruits. Pod development is rapid and lasts about 19 days.

Other botanical information

Within V. unguiculata the cultivated forms are classified as follows:

Cv.-group Unguiculata (sometimes V. 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 V. 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 V. 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.

Ecology

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 location. The optimum temperature for growth and development is between 20 and 35 °C. It can grow in a wide range of soils and does well on acid soils. Excess soil moisture reduces the crop growth, but drought can be tolerated.

Propagation

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 small-holdings. 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, sugar cane, and relay-cropped in standing rice. Cultivation practices differ widely in the region. In southern India, Sri Lanka, Philippines, Indonesia and Thailand most of the crop is grown after rice. During this period rainfall is diminishing, and later in the season soil moisture is limited. In rainfed 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, after which rice is transplanted. For catjang cowpea seedrate is 15-20 kg/ha in sole cropping, but lower in intercropping. Yard-long bean is grown on rice bunds as well as 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 ranges from 60 000-70 000 plants/ha.

Husbandry

Most cowpea crops are rainfed, a small proportion is irrigated, and others utilize 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 following 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 as well. 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, about 30 kg P₂O₅/ha often improve performance as may do a starter dose of N of 30 kg/ha. Cowpea is commonly incorporated in rotation systems in semi-arid, humid and subhumid environments.

Diseases and pests

Cowpea suffers from many viral, fungal and bacterial diseases. Major 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 important for integrated control. Diseases caused by fungi and bacteria are classified according to plant parts or growth stages most adversely affected. Major stem diseases in Africa include anthracnose (Colletotrichum lindemuthianum); major foliar diseases include a.o. 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 important 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 only important mycoplasm disease is phyllody. Cowpea is attacked by many insect pests throughout its geographical range, but in particular in Africa. The pests include aphids, beanfly, leaf hoppers, thrips, podborers, pod-sucking bugs, cowpea curculio, and storage weevils. In Africa, insect pests are often responsible for yield losses sometimes up to 100%. Major pests in Africa are: aphids (Aphis craccivora), thrips, pod bugs, pod borers (Maruca testulalis), and storage weevils (Callosobruchus spp.). In Asia major pests appear 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.

Harvesting

Green pods are harvested by hand when they are still immature and tender (12-15 days after flowering). The duration of pod picking may vary from 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. Therefore, they are handpicked now and then. Sometimes plants are pulled out 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.

Yield

Under subsistance agriculture in Africa average seed yield ranges between 100 and 300 kg/ha. When grown as a sole crop with good management, cowpea can produce yields varying from about 1000 to 4000 kg/ha. Largest yields have been achieved by crops relatively late to flower and mature. Dry seed yields in South-East Asia are usually higher than in West Africa. Yields of catjang cowpea in India vary between about 1000 to 2500 kg/ha. Green pod yield of yard-long bean can vary from 6 to 8 t/ha.

Handling after harvest

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 locally sold and consumed. Considerable quantities of cowpeas are processed in the USA. Yard-long beans may be quick-frozen, but, since the pods wilt very 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).

Genetic resources

The most extensive collection of germplasm is maintained at the International Institute of Tropical Agriculture, Ibadan, Nigeria, with about 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 ofVigna unguiculata.

Breeding

Insect pests and pathogens are the principal factors limiting productivity throughout Africa, whereas both photoperiod sensitivity and intermediate plant types are important 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 important for the production of cowpeas in semi-arid 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 Ba√±os, 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 cowpea forms existing in Southern Africa, are promising for improvement programs.

Prospects

The prospects for V. unguiculata are reasonably good through crop improvement and better management practices. Efforts on genetic resources and utilization 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.

Literature

Duke, J.A., 1981. Handbook of Legumes of world economic importance. Plenum Press, New York. p. 298-306.
Kay, D.E., 1979. Food Legumes. Crop Production Digest No. 3. Tropical Products Institute, London. p. 11-16, 86-114.
Lush, W.M. & Evans, L.T., 1981. Domestication and improvement of cowpea. Euphytica 30: 579-587.
Maréchal, R., Mascherpa, J.-M. & Stainier, F., 1978. Etude taxonomique d'une groupe complexe d'espèces des genres Phaseolus et Vigna (Papilionaceae) sur la base de donn√©es morphologiques et polliniques, traitées 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. 460 pp.

Authors

R.K. Pandey & E. Westphal