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Psophocarpus tetragonolobus (L.) DC.

Papilionaceae (Leguminosae - Papilionoideae, Fabaceae)
Chromosome number
2n = 18
Vernacular names
Winged bean, wing bean, asparagus pea, Goa bean (En). Pois carré, haricot ailé (Fr). Fava de cavalo (Po).
Origin and geographic distribution
Psophocarpus tetragonolobus is known only in cultivation; truly wild specimens have never been found. The greatest diversity is found in New Guinea and the hills of north-eastern India and neighbouring Myanmar (Burma), which are probable centres of domestication. Since the 1960s winged bean has been promoted strongly by international organizations as a multipurpose crop, and it has been introduced and tested in research stations in most countries of the tropics including those in tropical Africa. Yet at present it is only rarely found in home gardens or cultivated by farmers.
Immature fruits are most commonly used for consumption. They are tender but insipid and less appreciated than French bean or yardlong bean. The consumption of young leaves is quite common in Asia, either cooked or in salads. In Myanmar (Burma) and New Guinea, special cultivars are grown for the tuberous roots resembling small sweet potatoes. The international promotion of winged bean in research and extension focused on the nutritional value of the dry seed as a pulse, but this has not led to wide use. Much research has been devoted to processing and use of winged bean flour, e.g. as a protein supplement in bread-making and as animal feed. The seeds can be used for making edible oil, milk and fermented products similar to soya bean products, and the whole plant as well as processed seeds are good animal feed. Winged bean is sometimes found as an ornamental because of its attractive flowers. In tropical Africa these uses are rare. In fact only the use of the green fruits and occasionally leaves and dry seeds is relevant for tropical Africa.
Production and international trade
Winged bean is locally grown in home gardens in some African countries for domestic consumption. No data on production or trade are available.
The composition of young fruits per 100 g edible portion is: water 90 g, energy 113 kJ (27 kcal), protein 2.6 g, fat 0.5 g, carbohydrate 4.9 g, fibre 1.9 g, Ca 64 mg, Mg 34 mg, P 37 mg, Fe 0.8 mg, vitamin A 332 IU, thiamin 0.21 mg, riboflavin 0.1 mg, niacin 0.8 mg, ascorbic acid 15 mg (Rubatzky, V.E. & Yamaguchi, M., 1997). The composition of leaves per 100 g edible portion is: water 76.9 g, energy 310 kJ (74 kcal), protein 5.9 g, fat 1.1 g, carbohydrate 14.1 g, Ca 224 mg, Mg 8 mg, P 63 mg, Fe 4.0 mg, Zn 1.3 mg, vitamin A 8090 IU, thiamin 0.8 mg, riboflavin 0.6 mg, niacin 3.5 mg, folate 16 μg, ascorbic acid 45 mg. The composition of mature dry seeds per 100 g edible portion is: water 8.3 g, energy 1712 kJ (409 kcal), protein 29.7 g, fat 16.3 g, carbohydrate 41.7 g, Ca 440 mg, Mg 179 mg, P 451 mg, Fe 13.4 mg, Zn 4.5 mg, vitamin A 0 IU, thiamin 1.0 mg, riboflavin 0.45 mg, niacin 3.1 mg, folate 45 μg, ascorbic acid 0 mg. The composition of the tubers per 100 g edible portion is: water 57.4 g, energy 620 kJ (148 kcal), protein 11.6 g, fat 0.9 g, carbohydrate 28.1 g, Ca 30 mg, P 45 mg, Fe 2.0 mg, vitamin A 0 IU, thiamin 0.4 mg, riboflavin 0.15 mg, niacin 1.6 mg, folate 19 μg, ascorbic acid 0 mg (USDA, 2002).
The food value of winged bean fruits is comparable to that of French bean and yardlong bean, and that of the leaves to other dark green leafy vegetables. The composition of the seed is comparable to soya bean, its amino acid spectrum being similar. Improved cultivars with up to 37% protein in the seed exist. The lysine and threonine content is high, while methionine and cystine are limiting amino acids. The oil resembles that of groundnut. Oleic and linoleic acids make up about 67% of the total fatty acid component and saturated fatty acids 29%. The easily refined oil is reasonably stable, with a high tocopherol content.
The seed contains several potent proteinase inhibitors active e.g. in Heliothis armigera. It has been suggested that transfer of the relevant genes to other crops may make these resistant to the caterpillar, for which chemical control is becoming increasingly difficult.
Adulterations and substitutes
In vegetable dishes other leguminous fruits may as well be used, e.g. pods of French bean, pea, cowpea or yardlong bean. The dry seeds may be replaced by soya bean, lima bean, cowpea or other pulses. The edible leaves of the wild and cultivated African winged bean (Psophocarpus scandens (Endl.) Verdc.) can be used as substitutes for the leaves of winged bean.
Perennial climbing or twining herb, usually grown as an annual; roots numerous, with long lateral roots running horizontally at shallow depth, and some becoming thick and tuberous; stem up to 4 m long, ridged and glabrous. Leaves alternate, 3-foliolate; stipules ovate -lanceolate, c. 1 cm long, spurred, persistent; petiole 3–12 cm long, rachis 1.5–5.5 cm long; leaflets ovate-triangular, 4–15 cm × 3.5–12 cm, truncate to rounded at base, acute at apex, glabrous or glabrescent on both surfaces. Inflorescence a 2–10-flowered pseudoraceme; peduncle 5–15 cm long, rachis 1–10 cm long, slightly pubescent; bracts semi-caducous, minute, bracteoles persistent, up to 0.5 cm long. Flowers bisexual, papilionaceous; pedicel up to 5 mm long, slightly pubescent; calyx with tube 4–6 mm long, lobes unequal, up to 2 mm long, green to dark red -purple; corolla blue, mauve, creamy or reddish, with almost circular to broadly oblong standard up to 4 cm × 3.5 cm, emarginate, wings and keel slightly shorter; stamens 10, 9 with fused filaments and 1 free or somewhat connate in the middle; ovary superior, oblong, 1-celled, style bent, with a row of hairs below the stigma. Fruit an oblong to linear-oblong pod, square in cross -section, 6–40 cm × 2–3.5 cm, prominently 4-winged, glabrous, 5–21-seeded. Seeds almost globose, 0.5–1 cm in diameter, yellow, brown or black, sometimes white, sometimes mottled, glabrous, with a small aril. Seedling with epigeal germination.
Other botanical information
Psophocarpus comprises about 10 species, all native to tropical Africa, except Psophocarpus tetragonolobus. Some authors consider the wild Psophocarpus grandiflorus R.Wilczek, others Psophocarpus scandens (Endl.) Verdc. (African winged bean), as progenitor of Psophocarpus tetragonolobus. Psophocarpus palustris Desv. is also closely related. However, it has also been suggested that Psophocarpus tetragonolobus developed from an extinct wild Asian species. It is characterized by its comparatively large flowers, short bracteoles and glabrescent leaves, and by its often long fruits.
Growth and development
Emergence of the seedling under field conditions occurs 5–7 days after sowing. Temperatures around 25ºC appear most suitable for germination and growth. The fibrous root system with large N-fixing nodules (up to 1.5 cm in diameter) grows in proportion to the shoot until about 3 months after planting. In tuberous cultivars, increases in root dry weight continue beyond the 6th month after planting. After about 2 months the plants start flowering, although some local cultivars require as long as 5 months. The flowers are mostly self-pollinated. Fruit development is not greatly affected by environmental conditions. Maximum fruit length and maturity occur about 20 days and 65 days after pollination, respectively.
Winged bean is best adapted to equatorial climates. It is cultivated from sea-level up to 2000 m altitude, but does not tolerate night frost. Day temperatures of 25–32ºC and night temperatures above 18ºC are optimal for growth and reproductive development. Tuber initiation is favoured by cooler conditions. Winged bean requires at least 1000 mm annual rainfall, but is intolerant to waterlogging. Winged bean is a quantitative short-day plant, flower induction requiring a critical daylength of around 12 hours. The response to daylength varies with genotype, temperature and light intensity; some cultivars are day neutral. Winged bean thrives on a range of soil types with a pH above 5.5.
One or two weedings in the first 4–6 weeks are needed as early growth is slow. Staking is necessary; the yield is reduced to less than half if plants are grown creeping. In gardens winged bean is grown against stakes or trellises of about 2 m high. Irrigation is needed during periods of prolonged drought. Winged bean is known to nodulate profusely in symbiotic association with Rhizobium. In a well-nodulated crop, nitrogen application is not necessary. However, in soils low in nitrogen, small quantities of N fertilizer may be applied at planting. Winged bean needs fertile soil, and appropriate fertilizing with P and K is needed. Mulching is recommended in dry conditions.
Propagation and planting
Winged bean is normally propagated by seed, but tubers may also be used. The seeds are very hard and can be kept for several years, but old seed requires scarification before planting. Sowing 2–3 seeds per hole can be practised on raised beds; spacings are 40–60 cm in the row and 90–100 cm between rows. The 1000-seed weight is about 250 g; seed requirement 10–15 kg/ha. In home gardens winged bean is sown against walls, fences, trees or shrubs, and it may climb up to several metres high. Adequate drainage is essential and under wet conditions raised beds may be necessary.
Diseases and pests
Winged bean is not much affected by pests and diseases, and chemical spraying or other control measures are rarely applied. False rust or orange gall (Synchytrium psophocarpi) is perhaps the most widespread and damaging fungus. Cultivar resistance has been reported. Dark leaf spot (Pseudocercospora psophocarpi) is serious in hot humid areas. Powdery mildew (Erysiphe cichoracearum) occurs in cooler areas during periods of high air humidity in the dry season. Other diseases are web blight (Rhizoctonia solani) and flower blight (Choanephora cucurbitarum). Ring spot mosaic virus and necrotic mosaic virus were identified on winged bean in Côte d’Ivoire. Root-knot nematodes (Meloidogyne spp.) may cause stunted growth and yellowing of leaves. Amongst insect pests, bean pod-borer (Maruca testulalis) and various leaf-feeding caterpillars, bugs and cicadellids have been reported.
Fresh fruits are harvested when they reach about 80% of their full length, once or twice per week for several months. The leaves are mainly picked before the fruit setting period. Harvesting the mature seeds needs many rounds of picking of the dry fruits at regular intervals because fruit ripening occurs over a long period and the fruits split and shatter seeds when they remain too long on the plants. Tubers are harvested at the first signs of senescence of the crop.
Green fruit yields range from 10–15 t/ha, but up to 35 t/ha has been reported. Seed yield estimates from farmers’ crops reach 800–1500 kg/ha; experimental yields of more than 2 t/ha have been reported, with a maximum of 4.5 t/ha in an experiment in Malaysia. Tuber yield in farmers’ plots in Papua New Guinea was estimated at 5.5–12 t/ha.
Handling after harvest
Freshly harvested green fruits store poorly and should be marketed within 24 hours. Storage in a cool room at 10ºC and a relative humidity above 90% is possible. The leaves can be dried for long-term conservation. The dry seeds store very well, better than most pulses, due to their resistance to common storage insect pests. Tubers can be kept for up to 2 months, but they are normally consumed soon after harvesting.
Genetic resources
Large germplasm collections have been made from most parts of southern and eastern Asia and New Guinea. Collections are available at the National Bureau of Plant Genetic Resources (NBPGR), New Delhi, India, holding about 1100 accessions of Psophocarpus, the National Plant Genetic Resources Laboratory (IPB/UPLB), Los Baños, the Philippines (about 900 accessions), the Department of Genetics and Cellular Biology, University Malaya, Kuala Lumpur, Malaysia (about 450 accessions) and the Department of Agriculture, Papua New Guinea University of Technology, Lae, Papua New Guinea (about 450 accessions).
Several cultivar trials, but no breeding have been recorded for winged bean in tropical Africa. In Asia many local cultivars of the vegetable type occur. Several improved cultivars are available from the above mentioned institutes, but mainly for use as a pulse crop. Breeding objectives depend on the product for which winged bean is raised. As a green vegetable crop, early flowering, high fruit yield and production over a longer period of time, green fruit colour, less fibrousness (reduced parchment layers) and a better taste are desirable. As a pulse crop, important objectives are early flowering, synchronization of fruit maturity, senescence at the end of the growing season, high seed yield, low shelling percentage, high protein and oil content depending upon the processing needs, and white seed colour. For a tuber crop, selection for low fruit yield, vigorous vegetative growth, high tuber yield and tuber quality factors including high protein and low fibre content and acceptable flavour are relevant. Attempts to realize interspecific hybridization with other Psophocarpus species have been unsuccessful so far.
The introduction of winged bean as new pulse crop or as a multipurpose vegetable in tropical Africa was not successful, some reasons being the climbing plant habit needing staking, the bothersome seed harvesting and the seed shattering and seed hardness. These characteristics make winged bean less interesting than traditional pulses like cowpea and introduced pulses like soya bean and common bean. For consumers winged bean fruits are less attractive than yardlong bean and French beans because of the bland taste. Yet, winged bean as vegetable merits some attention as a nutritious and easy to grow garden crop, especially suited for home gardens.
Major references
• Eagleton, G.E., Khan, T.N. & Erskine, W., 1985. Winged bean (Psophocarpus tetragonolobus (L.) DC.). In: Summerfield, R.J. & Roberts, E.H. (Editors). Grain legume crops. Collins, London, United Kingdom. pp. 624–657.
• Harder, D.K. & Smartt, J., 1992. Further evidence on the origin of the cultivated winged bean, Psophocarpus tetragonolobus (L.) DC. (Fabaceae): chromosome numbers and the presence of a host-specific fungus. Economic Botany 46(2): 187–191.
• Khan, T.N., 1982. Winged bean production in the tropics. FAO Plant Production and Protection Paper 38. FAO, Rome, Italy. 217 pp.
• Khan, T.N., 1993. Psophocarpus tetragonolobus (L.) DC. In: Siemonsma, J.S. & Kasem Piluek (Editors). Plant Resources of South-East Asia No 8. Vegetables. Pudoc Scientific Publishers, Wageningen, Netherlands. pp. 229–233.
• Mnebuka, B.V. & Eggum, B.O., 1995. Comparative nutritive value of winged bean (Psophocarpus tetragonolobus) and other legumes grown in Tanzania. Plant Foods for Human Nutrition 47(4): 333–339.
• Rubatzky, V.E. & Yamaguchi, M., 1997. World vegetables: principles, production and nutritive values. 2nd Edition. Chapman & Hall, New York, United States. 843 pp.
• Tindall, H.D., 1983. Vegetables in the tropics. Macmillan Press, London, United Kingdom. 533 pp.
• USDA, 2002. USDA nutrient database for standard reference, release 15. [Internet] U.S. Department of Agriculture, Beltsville Human Nutrition Research Center, Beltsville Md, United States. http://www.nal.usda.gov/fnic/foodcomp. Accessed June 2003.
• Verdcourt, B. & Halliday, P., 1978. A revision of Psophocarpus (Leguminosae – Papilionoideae – Phaseolae). Kew Bulletin 33(2): 191–227.
Other references
• Asare, E., 1984. The growth of the winged bean (Psophocarpus tetragonolobus (L) DC.). MSc thesis, Department of Crop Science, Faculty of Agriculture, Kwame Nkruma University of Science and Technology, Kumasi, Ghana. 129 pp.
• Eagleton, G., 1999. Winged bean in Myanmar, revisited. Economic Botany 53: 342–352.
• Giri, A.P., Harsulkar, A.M., Ku, M.S.B., Gupta, V.S., Deshpande, V.V., Ranjekar, P.K. & Franceschi, V.R., 2003. Identification of potent inhibitors of Helicoverpa armigera gut proteinases from winged bean seeds. Phytochemistry 63: 523–532.
• Kemevor, G.L.A., 1980. Evaluation of exotic germplasm of winged bean (Psophocarpus tetragonolobus). BSc thesis, School of Agriculture, University of Cape Coast, Cape Coast, Ghana. 52 pp.
• Kpodo, C.M., 1987. A general survey of insects associated with winged bean (Psophocarpus tetragonolobus (L.) DC.). BSc thesis, School of Agriculture, University of Cape Coast, Cape Coast, Ghana. 45 pp.
• Trèche, S., Tobias, J.F., Noubi, L., Pasquet, R. & Fotso, M., 1986. Composition chimique des différents organes du haricot ailé (Psophocarpus tetragonolobus). Revue Science et Technique. Série Sciences de la Santé (CMR) 3(1–2): 117–136.
Sources of illustration
• Khan, T.N., 1993. Psophocarpus tetragonolobus (L.) DC. In: Siemonsma, J.S. & Kasem Piluek (Editors). Plant Resources of South-East Asia No 8. Vegetables. Pudoc Scientific Publishers, Wageningen, Netherlands. pp. 229–233.
G.J.H. Grubben
Prins Hendriklaan 24, 1401 AT Bussum, Netherlands
Based on PROSEA 8: ‘Vegetables’.

G.J.H. Grubben
Prins Hendriklaan 24, 1401 AT Bussum, Netherlands
O.A. Denton
National Horticultural Research Institute, P.M.B. 5432, Idi-Ishin, Ibadan, Nigeria
Associate Editors
C.-M. Messiaen
Bat. B 3, Résidence La Guirlande, 75, rue de Fontcarrade, 34070 Montpellier, France
R.R. Schippers
De Boeier 7, 3742 GD Baarn, Netherlands
General editors
R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
L.P.A. Oyen
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
PROSEA Network Office, Herbarium Bogoriense, P.O. Box 234, Bogor 16122, Indonesia
Photo Editor
E. Boer
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article:
Grubben, G.J.H., 2004. Psophocarpus tetragonolobus (L.) DC. In: Grubben, G.J.H. & Denton, O.A. (Editors). PROTA 2: Vegetables/Légumes. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, part of flowering branch; 2, tuber; 3, fruit; 4, seed.
Source: PROSEA


fruiting plant habit