Canavalia gladiata (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Canavalia gladiata (Jacq.) DC.

Protologue: Prodromus 2: 404 (1825).

Family: Leguminosae

Chromosome number: 2n= 22, 44.

• Dolichos gladiatus Jacq. (1787),
• Canavalia ensiformis (L.) DC. var. gladiata (Jacq.) Kuntze (1898),
• C. ensiformis auct. non (L.) DC.

• Sword bean (En)
• Pois sabre (Fr)
• Indonesia: kara pedang, kacang parasman, koas bakol
• Malaysia: kacang parang, kacang polong
• Philippines: habas (Tagalog), magtambokau (Bisaya)
• Cambodia: tioeuhs
• Laos: (khùa) 'khao 'khièo
• Thailand: thua-phra
• Vietnam: dậu rựa.

Sword bean is of Asiatic or African origin. It is only known in cultivation and is probably derived from C. virosa (Roxb.) Wight & Arnott, the most closely related wild species, occurring mainly in Africa. Sword bean is widely cultivated in South and South-East Asia, especially in India, Sri Lanka, Burma and Indo-China. It has now spread throughout the tropics and has become naturalized in some areas.

Sword bean is used as vegetable, cover crop, forage and green manure. The young green pods are extensively eaten in tropical Asia, served as a boiled green vegetable similar to common bean (Phaseolus vulgaris L.). The full-grown but still fresh, green seeds are consumed as a cooked vegetable similar to broad bean (Vicia faba L.). Sword bean is not a popular pulse because of the strong flavour and the thick, tough seed-coat. Dry, fully mature seeds should be eaten with caution as they may be somewhat poisonous. Detoxification by changing the cooking water, soaking, rinsing or fermentation is possible but laborious. White seeds are considered to have a better flavour than coloured seeds.

Both the flowers and young leaves are used steamed as a flavouring. In Java sword bean is used as a short-duration cover crop and as a green manure. It is occasionally used as fodder but less so than the related jack bean (C. ensiformis (L.) DC.). Pink seeds are sometimes employed in traditional Chinese medicine. The urease extracted from sword beans is used in analytical laboratories.

Sword bean is a small-scale vegetable crop, the fresh product being home-consumed or marketed locally. The dry, mature seeds are not an important product of commerce.

The young green pods and the unripe fresh seeds are rather similar in composition and contain per 100 g edible portion: water 88.6 g, protein 2.7 g, fat 0.2 g, carbohydrates 6.4 g, fibre 1.5 g, ash 0.6 g, vitamin A 40 IU. The energy value is 160 kJ/100 g.

The use of sword bean is limited because of the growth-inhibiting compounds canavalin, concanavalin A and B, urease and canavanine. Toxicity seems largely due to concanavalin A, which binds to mucosal cells of the intestine, thus reducing the body's ability to absorb nutrients from the intestine.

1000-seed weight is 1000-4000 g.

• A vigorous, woody, perennial climber, 3-10 m long, often grown as an annual.
• Root system deeply penetrating the soil.
• Leaves trifoliolate, petiole 5-17 cm long, petiolules 4-7 mm; leaflets ovate, 7.5-20 cm × 5-14 cm, acuminate, sparsely pubescent on both surfaces.
• Inflorescence an axillary raceme, 7-12 cm long, peduncle 4-20 cm long, pedicels 2 mm long; flowers often reflexed; calyx up to 16 mm long; standard ca. 3.5 cm long, white.
• Fruit a legume, linear-oblong, slightly compressed, 15-40 cm × 2.5-5 cm, widest near the apex, sometimes curved with strongly developed ridges, containing 8-16 seeds.
• Seeds oblong-ellipsoid, strongly compressed, 2-3.5 cm × 1.5-2 cm, pink, red, reddish-brown to almost black, rarely white; hilum 1.5-2 cm long, dark brown; seed-coat very tough and thick.

Sword bean seed germinates readily and the plant is relatively fast-growing. The flowers are visited by bees and 20% or more cross-pollination occurs. Young pods for vegetable use are available 3-4 months after sowing, mature seeds can be harvested 5-10 months after sowing.

Cultivars vary widely, particularly in the degree of twining, the size of the pods and the number and colour of the seeds. In some areas semi-erect forms are found. Forms with red or reddish to blackish seeds are sometimes classified as C. gladiata var. gladiata and forms with white seeds as var. alba (Makino) Hisauchi.

C. gladiata is often confused with C. ensiformis because their vegetative parts and flowers are very similar. However, they can be distinguished by their pods and seeds. In C. ensiformis the pod is usually more than 8 times as long as broad (in C. gladiata less than 8 times), and the hilum is less than half the length of the seed (in C. gladiata more than half the length of the seed). C. ensiformis is of New World origin.

Sword bean requires a tropical climate. It grows well at temperatures of 20-30 °C and is cultivated from sea-level up to 1000 m altitude. Its deep root system allows sword bean to survive dry conditions, but it fares best with an evenly distributed rainfall of 900-1500 mm/year. It grows well on the very leached, nutrient-depleted, lowland tropical soils and on acid soils with a pH of 4.5-7.0. It is more resistant to saline soils and less affected by waterlogging or drought than many other legumes. It also tolerates some shade.

Sword bean is usually grown near houses and allowed to trail on walls, fences and trees. It is propagated by seed, sown at a depth of 5-7.5 cm, at seed rates of 25-40 kg/ha. Plants are usually spaced 45-60 cm apart, in rows 75-90 cm apart. Sword bean is rather resistant to attack from diseases and pests. The most serious fungal disease is root rot (Colletotrichum lindemuthianum). Major pests are fall army worm (Spodoptera frugiperda) and beetle grubs that bore into the stems. At the end of the season, the crop should be dug up and burned. If grown as a perennial it is recommended that plants are kept not more than two years.

Green pods are normally hand-picked when they are 10-15 cm long, before they swell and become fibrous and tough. Mature pods are also harvested by hand to avoid shattering. Yields of green pods may reach 4 t/ha. Experimental yields as high as 4600 kg/ha of dry seed have been recorded, but farm yields average 700-900 kg/ha. Yields of green matter for forage are 40-50 t/ha. Stored seeds are rather resistant to infestation by pests.

There are no breeding programmes for sword bean. Some cultivars which show reduced toxicity have been selected. However, a programme for worldwide collection of germplasm is needed, followed by mass screening for cultivars containing no concanavalin A and other toxic constituents.

Sword bean is a minor vegetable crop and its use for human as well as animal consumption requires caution. The presence of toxic substances makes it unlikely that this bean will increase much in importance in the short term. However, because of its uncommon adaptability to adverse conditions, resistance to diseases and pests, and relatively high productivity, sword bean might be used as a reclamation crop on marginal lands, and therefore deserves more research attention.

• Duke, J.A., 1981. Handbook of legumes of world economic importance. Plenum Press, New York/London, United States/United Kingdom. pp. 41-43.
• Herklots, G.A.C., 1972. Vegetables in South-East Asia. George Allen & Unwin, London, United Kingdom. pp. 233-236.
• Kay, D.E., 1979. Food Legumes. TPI Crop and Product Digest No 3. Tropical Products Institute, London, United Kingdom. pp. 365-370.
• National Academy of Sciences, 1979. Tropical legumes, resources for the future. National Academy of Sciences, Washington, D.C., United States. pp. 54-59.
• Nguyên van Thuân, 1979. Légumineuses - Papilionoïdées, Phaséolées. Canavalia. In: Flore du Cambodge, du Laos et du Vietnam [Flora of Cambodia, Laos and Vietnam] (various editors). Muséum National d'Histoire Naturelle, Laboratoire de Phanérogamie, Paris, France. Vol. 17. pp. 71-77.

• G. Kooi