Vigna unguiculata (PROSEA Vegetables)

Plant Resources of South-East Asia
Introduction

Vigna unguiculata (L.) Walp. cv. group Sesquipedalis

Protologue: Repert. bot. syst. 1: 779 (1843). Cv. group Sesquipedalis: Westphal. Pulses in Ethiopia, their taxonomy and agricultural significance. p. 227 (1974).

Family: Leguminosae

Chromosome number: 2n= 22

Synonyms

Dolichos sesquipedalis L. (1763),
Vigna sesquipedalis (L.) Fruhw. (1898),
V. sinensis (L.) Hassk. ssp. sesquipedalis (L.) van Eseltine (1931),
V. unguiculata (L.) Walp. ssp. sesquipedalis (L.) Verdc. (1970).

Vernacular names

Yard-long bean, long bean, asparagus bean, snake bean (En)
Dolique asperge, haricot kilomètre (Fr)
Indonesia: kacang panjang, kacang usus, kacang belut
Malaysia: kacang panjang, kacang belut, kacang perut ayam
Philippines: sitao (Tagalog), hamtak (Bisaya), utong (Ilocano)
Cambodia: sândaèk troeung
Thailand: tua fak yaow
Vietnam: dậu dựa, dậu giải áo.

Origin and geographic distribution

Yard-long bean very probably originated in East or South-East Asia, possibly from southern China in view of the large genetic diversity in this area. It is one of the top 10 vegetables in importance in all South-East Asian countries, Taiwan, southern China and Bangladesh. Yard-long bean is of much less importance in India and the Pacific. In the Philippines its importance is decreasing in favour of "bush sitao", a crossing between yard-long bean and cowpea (cv. group Unguiculata), probably because "bush sitao" does not need trellis and is less susceptible to wind damage. Yard-long bean spread with emigrants from South-East Asia to many countries in other tropical areas, where it is cultivated as a minor vegetable. It is quite popular in the Caribbean area and is produced as a summer crop in southern California. It is grown as a specialty greenhouse crop in the Netherlands.

Uses

The succulent young pods of yard-long bean are used as a cooked vegetable, mostly combined with rice as the main dish. There are many preparation methods with various spices. Yard-long bean is an important ingredient of many vegetable soups. In Indonesia the consumption of fresh young pods in salads (lalab) is very popular. The consumption of mature dry seed as pulse comparable with cowpea (other cv. groups of V. unguiculata) is possible but unusual. The consumption of shoots and young leaves as leafy vegetable is popular in Indonesia and elsewhere.

Production and international trade

Reliable statistics on yard-long bean are scarce because most of the crop is grown for home consumption; moreover, in statistics they are often combined with other leguminous vegetables. They are not included in FAO statistics. The area annually cultivated with yard-long bean in Indonesia (1988) is 97 000 ha, production 281 000 t. In Thailand (1988) about 10 000 ha of yard-long bean are grown, yielding 75 000 t. Yard-long bean is an important market vegetable in all South-East Asian countries where it is extensively grown in home gardens, on dikes around paddy fields and in fields in sole or mixed intercropping. It is a typical smallholder crop. Although yard-long bean is one of the most common vegetables on local markets, the quantity exported is insignificant.

Properties

The composition per 100 g edible portion (pods) is: water 89 g, protein 3.0 g, fat 0.5 g, carbohydrates 5.2 g, fibre 1.3 g, ash 0.6 g, Ca 64 mg, P 54 mg, Fe 1.3 mg, vitamin A 167 IU, vitamin B₁ 0.07 mg, vitamin C 28.0 mg. The energy value is 125 kJ/100 g. The rather high nutritional value, combined with the high level of intake, make yard-long bean a very important vegetable in the diet of South-East Asian people. The nutritional composition of yard-long bean is roughly comparable with French bean (Phaseolus vulgaris L.). The composition of the leaves is comparable with leafy vegetables like amaranth. The 1000-seed weight varies from 150-250 g.

Description

A climbing, nearly glabrous annual, 2-4 m long, with well developed root system. Stems twining, 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-)7-13.5(-19.5) cm × (3.5-)4-9.5(-17) cm.
Inflorescence an axillary raceme with several yellowish or pale-blue 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; bract 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 × 12 mm, keel boat-shaped, 21 mm × 12 mm; stamens diadelphous (9 + 1); ovary with 12-21 ovules.
Pod pendent, 30-120 cm long, more or less inflated and flabby when young, constricted when mature, 10-30-seeded.
Seed elongated, more or less cylindrical to rounded, variable in size and colour, usually 8-12 mm long, reddish-brown or black with a white hilum.
Seedling with epigeal germination.

Growth and development

Yard-long bean seeds sown in moist earth of over 22 °C germinate in 3-5 days. After germination, growth is very fast. Flowering starts in the 5th week after sowing and the harvest of young pods starts 2 weeks later. The degree of cross-pollination by insects is low in dry climates but may amount to 40% in locations with high relative air humidity. Depending on the crop health and intensity of harvesting, senescence starts 1½-2 months after sowing and the plant dies after 3-4 months.

Other botanical information

The typical feature of cv. group Sesquipedalis is the long, slack, pendent pod, which requires a climbing growth habit; the dry seeds are rarely consumed. It should not be confused with the "catjang cowpea" which belongs to the cv. group Biflora, characterized by erect or ascending, short (10-15 cm), firm and succulent pods, not inflated when young, with plant habit erect or spreading, although semi-viny and climbing cultivars needing staking also occur. Not only the young pods and young seeds but also the mature dry seeds of cv. group Biflora are harvested and consumed like normal cowpea (cv. group Unguiculata). The so-called "bush sitao" has become a popular vegetable in the Philippines. This cross between cowpea and yard-long bean has fleshy pods, 15-30 cm long, borne in pairs at the end of long peduncles arising above the canopy. It is a type of vegetable cowpea which may also be included in cv. group Biflora.

In Malaysia, comparison of yard-long bean and vegetable cowpea types showed that staked yard-long bean was more productive (18-25 t/ha in 14 weeks) than the bush types (3-4 t/ha in 11 weeks) and the pods were more tender and palatable. Advantages of the short stiff pods of vegetable cowpea are the easier handling and packing for supermarkets compared to yard-long bean.

There are many landraces or cultivars within cv. group Sesquipedalis, mainly distinguishable by the characteristics of the young pods in the harvest stage. Other important cultivar features are: growth vigour and colour of the leaves, flowers and seed. A well known Indonesian cultivar is "Usus Hijau" with dark green pods 60-80 cm long, succulent and regularly shaped, tolerant to pod-borer, anthracnose and witches' broom virus. Several cultivars derived from local landraces or farmers' selections are offered by private seed companies in the various countries.

Ecology

Yard-long bean cultivars are daylength neutral or they may show a slight short-day reaction. They perform best under full sunlight but tolerate some shade. Day temperatures between 25-35 °C and night temperatures not below 15 °C are required, which means that cultivation is restricted to low and medium elevations. At elevations above 700 m growth is retarded. In fact French bean and yard-long bean are more or less complementary in this respect, the former being cultivated mainly at higher altitudes and in the lowlands during the cool season. However, there is a certain overlap; at medium elevations in Java and in the lowlands in Thailand and Vietnam both species may be found in the same field.

Yard-long bean performs well under humid conditions since it is not very susceptible to fungal diseases. The water requirement of the full grown crop is high, 6-8 mm per day. Cultivation in the dry season with ample irrigation is practised, as well as cultivation during the rainy season, provided that the drainage is adequate. Sowing during the rainy season may lead to damage to the emerging or young plants. The crop performs reasonably well on wet soils but an abrupt period of waterlogging causes serious damage and yield reduction. All soil types from light sandy or latosol to heavy clay are used, with a pH of 5.5-7.5. It is tolerant of slightly acid soil.

Propagation and planting

Many farmers use the seed harvested from a previous crop. At the end of the harvest period they merely leave a sufficient number of pods to ripen. The dry seeds, which show no dormancy, are sown directly in hills (pockets) of 2-4 seeds. Cultivation is usually on raised beds for good drainage and easy surface irrigation and for easy staking and harvest. A common system consists of beds 1.2-1.5 m wide with double rows at 60-90 cm and 20-40 cm between the hills, leading to a density of 40 000-60 000 hills/ha. For sole cropping the amount of seed needed is 15-40 kg/ha. When planted on dikes and open spaces in other crops, the hills may be spaced the same distance (20-40 cm).

Earthing-up the young plants protects the shallow root system and gives some support to the seedlings. Some farmers apply a mulch of rice straw, but this is not a common practice.

Husbandry

Yard-long bean has the same fertilizer requirements as the better known French bean. The recommendation for Indonesia is to apply 5-10 t/ha of farmyard manure during soil preparation, together with 50 kg/ha of urea, 50 kg/ha of KCl and 100 kg/ha of triple superphosphate.

Stakes 200-250 cm long are inserted near the seed stations before sowing or during the first two weeks after emergence (before the plants have reached a height of 30 cm). The method of staking varies, depending on the custom of the area, and is sometimes combined with ropes or wire. A cheap method of staking is to sow yard-long bean besides the stems of maize before or just after the cobs are harvested. Weeding by superficial hand hoeing is only needed during the first month. Once the crop is fully grown it outcompetes weeds.

Three weeks after emergence a top dressing of 50 kg/ha urea is given, applied around the hills. The plants have to rely on their own N production for additional nitrogen. Seed is sometimes inoculated with Rhizobium, but this is not necessary on land previously used for leguminous vegetables. On fertile soils fertilization should be reduced, because if growth is too luxuriant pod set will be poor and the crop will be very susceptible to diseases and pests.

Diseases and pests

The most damaging diseases are rust (Uromyces vignae), mildew (Erysiphe polygoni) and viruses such as cowpea aphid-borne mosaic virus and cowpea witches' broom virus. Control of the virus vectors (aphids, whiteflies, beetles and leafhoppers) and the removal of infected plants will help to keep virus diseases under control. Also common are Cercospora leaf-spot and anthracnose (Colletotrichum lindemuthianum), whereas bacterial blight (Pseudomonas phaseoli) is rarely a problem. The fungal diseases are more troublesome during the rainy season, whereas the insect pests, mites and virus diseases cause more damage during the dry season. For the control of virus diseases, fungal diseases (anthracnose) and bacterial diseases (Pseudomonas), it is very important to use healthy seed. No resistant cultivars are known.

The bean shoot fly Ophiomyia phaseoli is a common pest. The larvae tunnel in the leaves and stems. Severely attacked young plants will die and older plants will suffer from hampered growth and serious yield reduction. Another common pest is the bean pod fly Melanogromyza sojae. The larvae damage the petioles and young pods. Control involves protecting the seed with a systemic insecticide, e.g. carbofuran at sowing or applied as a solution to the emerging plantlets in the planting holes. During an attack, spraying with insecticides is recommended. Plant debris and affected plants must be burned. Pod-borers Etiella zinckenella and Maruca testulalis sometimes cause damage and may be controlled by chemical spraying. Yard-long bean is very attractive to aphids (Myzus persicae, Aphis gossypii), green stink bug (Nezara viridula) and red spider mite (Tetranychus spp.). Greasy cutworms (Agrotis ipsilon) often cause damage just after emergence. Sometimes thrips may cause damage. Chemical control of insects is common practice, often as a weekly routine, by spraying with a mixture of pesticides. Because of the risks for the farmer and the consumer, these sprayings must be reduced to the strict minimum.

Harvesting

The first picking of young pods in the desirable stage takes place 6-7 weeks after planting. The best harvest stage depends on the cultivar and the market requirements. Normally the pods are picked when the outline of the seeds is just visible on the outside of the pod. Picking must be meticulous, because pods which are passed over until the next harvest will become tough and discoloured, with swollen seed which exhaust the plant. Successive harvests take place at least once a week (for a better tuned grading, twice a week) during 4-8 weeks.

Yield

A total yield of 15 t/ha is considered satisfactory, but yields as high as 30 t/ha have been reported. In 1988, the average yield in Indonesia was 2.9 t/ha, in Thailand 7.2 t/ha. An indication of the potential yield is offered by the results of greenhouse cultivation in the Netherlands: growers obtain up to 8 kg/m² of marketable pods in a summer growing season of 4 months.

Handling after harvest

The harvested beans are tied in bundles of 20-40 pods and packed in baskets or crates for transport to the market. Yard-long bean is less susceptible to loss of weight by transpiration and to transport damage than most other vegetables. In cool store (8° C) they will keep for 4 weeks.

Genetic resources

Small collections of yard-long bean are present at the Asian Vegetable Research and Development Center (AVRDC), Taiwan, the Lembang Horticultural Research Institute (LEHRI), Indonesia, the Malaysian Agricultural Research and Development Institute (MARDI), Malaysia, and the Institute of Plant Breeding at Los Baños, the Philippines. The Institute for Vegetable Research at Beijing, China, has an interesting collection. Yard-long bean makes up a small part of the cowpea collection of the International Institute of Tropical Agriculture (IITA), Nigeria. Since commercial cultivars are on the rise, the huge diversity of yard-long bean landraces is in danger of genetic erosion.

Breeding

Crop improvement has been done by some national research institutes and seed companies through selection and purification of landraces. Important selection criteria are yield capacity and market quality. Yield is strongly correlated with pod length and the number of pods per plant. In Malaysia, selections from landraces and line selection in crosses between local cultivars resulted in improved cultivars such as "Sabah Black" with a yield potential of 25 t/ha. More breeding work using hybridization with other cv. groups of V. unguiculata showing valuable resistances should be started. Resistance to bean flies would be most welcome but seems difficult to achieve. Resistance to fungus and virus diseases might possibly be found.

Prospects

Yard-long bean will remain one of the leading vegetables in South-East Asia. It may expand further to other tropical areas. It is possible that types with short stiff pods or the "bush sitao" (cv. group Biflora) become more important because of easier handling. More emphasis should be put on control of diseases and pests without chemicals.

Literature

Haryono Semangun, 1989. Penyakit-penyakit tanaman hortikultura di Indonesia [Diseases of horticultural crops in Indonesia]. Gadjah Mada University Press, Yogyakarta, Indonesia. pp. 80-88.
Heij, G., 1989. Research experiences with yardlong bean in glasshouses in the Netherlands. Acta Horticulturae 242: 305-311.
Herklots, G.A.C., 1972. Vegetables in South-East Asia. George Allen & Unwin, London, United Kingdom. pp. 260-267.
Knott, J.E. & Deanon Jr, J.R. (Editors), 1967. Vegetable production in South-East Asia. University of the Philippines Press, Los Baños, the Philippines. pp. 66-96.
Mak, C., 1987. Comparative performance of vegetable cowpea and long bean. Malaysian Applied Biology 16(1): 323-325.
Ochse, J.J. & Bakhuizen van den Brink, R.C., 1980. Vegetables of the Dutch East Indies. 3rd English edition (translation of "Indische Groenten", 1931). Asher & Co., Amsterdam, the Netherlands. pp. 435-439.
Subhan, Sudjoko, Suwandi & Zainal Abidin (Editors), 1989. Bercocok tanam sayuran dataran rendah [Growing lowland vegetables]. Lembang Horticultural Research Institute (LEHRI), Bandung, Indonesia. Chapter 5, pp. 1-6.
Tindall, H.D., 1983. Vegetables in the tropics. MacMillan, London, United Kingdom. pp. 296-299.

Authors

G.J.H. Grubben