Vigna hosei (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Vigna hosei (Craib) Backer

Protologue: Geïll. Handb. Jav. Theeonkr.: 153 (1924).

Family: Leguminosae - Papilionoideae

Chromosome number: 2n= 20

Synonyms

• Dolichos hosei Craib (1914),
• Vigna oligosperma Backer (1924, nom. nud.).

Vernacular names

• Sarawak bean (En)
• Indonesia: tolo lembut.

Origin and geographic distribution

V. hosei most probably originated in south-eastern Africa, but is now also found in the humid tropics of South-East Asia from Sri Lanka to Japan, and in Australia. It is also recorded from the United States. In South-East Asia it was first found in cultivation in Sarawak and taken from there to Peninsular Malaysia and later to Java. It is now cultivated in Malesia, Sri Lanka, East Africa and Surinam.

Uses

V. hosei is grown as a green manure and cover crop in young tree plantations; in Indonesia in rubber, tea and coconut, in Malaysia in rubber and oil palm, in Sri Lanka in coconut plantations. In Rwanda it is being tested as a green manure in association with annual crops. It is also used as a pasture legume.

Properties

The weight of 1000 seeds is about 27 g.

Description

• A twining or creeping vine often forming a thick ground cover. Root system shallow. Stem 1-2 m long, with scattered hairs, easily rooting at the nodes.
• Leaves alternate, trifoliolate; petiole 2-5 cm long; stipules linear, base cordate, long persistent; rachis 2.5-6 cm long; petiolule 1.5-3 mm long, hairy; leaflets ovate-elliptical to obovate-oblong, terminal leaflet 2-7.5(-9) cm × 1.5-5(-6) cm, laterals oblique, apex acute, rarely obtuse, base more or less rounded, both surfaces with sparse, long hairs.
• Inflorescence an axillary raceme, 2-8 cm long, bearing small, yellow, paired flowers; peduncle 1.5-7 cm long; pedicel about 2 mm long, appressed pubescent; bracteoles very small, early caducous.
• Calyx tubular, tube about 2 mm long, ending in 5 teeth, the 2 upper teeth connate, triangular, about 1 mm long; standard orbicular, 6-12 mm in diameter, yellow; ovary 2-4(-5)-locular, with densely appressed, long hairs.
• Pod, 1-2 cm × 4-4.5 mm, finely pubescent, black, usually containing 1-3(-4) seeds.
• Seed brown, blotched with dark brown.
• "Subterranean pod" 1-1.5 cm long, pale yellow, densely covered with fine hairs, 1-2-seeded, on up to 7 cm long peduncle.

Growth and development

Seedling growth is vigorous and young plants quickly suppress weed growth. Flowering occurs about 6 months after planting, self-pollination is the rule. Seed set is poor. Although non-specific in its Rhizobium requirement, inoculation is preferably carried out with a selected cowpea strain such as CB 756. V. hosei fixes significant amounts of atmospheric nitrogen and forms a dense leaf litter. Besides producing normal aerial flowers and pods, V. hosei also produces flowers and pods which are hidden under the litter of leaves covering the soil.

Other botanical information

Sometimes 2 varieties are distinguished mainly based on hairiness of stems and leaves: var. hosei is glabrescent, mainly found in South-East Asia; var. pubescens Maréchal, Mascherpa & Stainier is pubescent and occurs mainly in Africa.

V. hosei is very similar and probably closely related to V. parkeri Baker from Central and East Africa. The latter species has blue to violet flowers, never forms subterranean pods and has 22 chromosomes.

Ecology

V. hosei requires an annual rainfall of 2500 mm. Since it has a shallow root system, it has a low tolerance of drought but it can withstand flooding. It can be found up to 1100 m altitude in grassland and secondary forest, in both open and shaded locations. An outstanding characteristic is its persistence under shade, but full sunlight is required for good seed production. It is adapted to a wide range of soils, but prefers acid soils of pH 4.9 or less.

Propagation and planting

V. hosei can be propagated by seed and by cuttings. When sown as a cover crop it may be mixed with other leguminous covers such as Calopogonium mucunoides Desv., Centrosema pubescens Benth. and Pueraria phaseoloides (Roxb.) Benth. For satisfactory germination the seeds are scarified by immersing them in concentrated sulphuric acid for 10 minutes followed by repeated rinsing, or by soaking in hot water (75 °C) for 2 hours or in cold water for 3 days. Mechanical scarification is also possible. Prior to sowing, the seeds may be inoculated with compost containing an appropriate Rhizobium strain, and mixed with rock phosphate fertilizer equivalent to the weight of the seeds used. Seeds are sown in shallow furrows about 5 cm deep. About 2-3 drills are established in between rows of young plantation trees. A pre-emergence herbicide is sprayed along the drills after the seeds are covered. When establishing a pasture, a good seed-bed is prepared and 1 kg seeds per ha are drilled at a depth of 1.25 cm, followed by harrowing or rolling. V. hosei combines well with guinea grass (Panicum maximum Jacq.), pangola grass (Digitaria eriantha Steudel) and Brachiaria grasses. For vegetative propagation it is recommended to plant during the rainy season and to use 20 cm long, 3-noded cuttings planted 1-1.5 m apart.

Husbandry

Application of compound fertilizer (15% N, 15% P₂O₅, 6% K₂O and 4% MgO) at a rate of 30 g per 6 m drill is recommended 1 and 3 weeks after germination. Fertilizer should be applied during dry weather, to avoid scorching the foliage. At 3 and 6 months after sowing, rock phosphate is broadcast over the cover at a rate of 60 kg/ha. If a magnesium deficiency is expected, kieserite should be applied at 125 kg/ha. Hand weeding is carried out at 2-week intervals during the early establishment stage of the legume. It is common to have a relatively pure legume cover during the early growth of plantation trees, maintaining the cover until the tree canopy starts to shade it out. In rubber and oil-palm plantations the planting of leguminous cover crops has been shown to have beneficial effects on tree growth. As a pasture legume, V. hosei can be subjected to light grazing during the early stages of establishment. Once established it can tolerate heavy stocking. Seed production is often poor and only about 50 kg/ha can be harvested. Harvesting seed on a field scale is also difficult.

A cover of V. hosei can be removed easily by hoeing the soil, followed by a clean weeding.

Diseases and pests

As a cover crop, V. hosei is susceptible to a fungus disease ascribed to Rhizoctonia solani which causes wilting or damping-off of the leaves, the effect being that large patches of leaves die off. It may or may not regenerate, depending on weather conditions. Wet weather favours the spread of the disease. If the attack is severe, the affected patches may be sprayed with 0.2% ferbam. When replanting cleared rubber plantations, that were severely affected by root diseases, the cover may also suffer attacks by Fomes lignosus and Ganoderma pseudoferreum. Control by fungicides is not economical in such instances.

Most of the pests that can destroy cover crops are leaf eaters: caterpillars, beetles, bugs, grasshoppers, snails and slugs. The roots may be attacked by cockchafer grubs and root-knot nematodes. Control measures against these pests, especially chemical sprays, are considered unnecessary because they upset the natural balance.

Prospects

Due to its persistence under shade, V. hosei can enrich a mixture of leguminous covers for young plantation trees. Being a low-growing creeper, it hardly climbs trees, which is considered important for a good cover crop. Its persistence in sward-forming grasses also renders it a promising pasture legume.

Literature

• Backer, C.A. & van Slooten, D.F., 1924. Geïllustreerd handboek der Javaansche theeonkruiden en hunne beteekenis voor de cultuur [Illustrated handbook of weeds of Javanese tea plantations and their significance for tea-growing]. Ruygrok, Batavia, Dutch East Indies. pp. 153, 153a.
• Hacker, J.B., 1990. A guide to the herbaceous and shrub legumes of Australia. University of Queensland Press, St. Lucia, Australia.
• Maréchal, R., Mascherpa, J.-M. & Stainier, F., 1978. Etude taxonomique d'un groupe complexe d'espèces des genres Phaseolus et Vigna (Papilionaceae) sur la base de données morphologiques et polliniques, traitées par l'analyse informatique [Taxonomic study of a complex group of species of the genera Phaseolus and Vigna (Papilionaceae) on the basis of morphological and pollen data, analysed by computer]. Boissiera 28: 172-175.
• Skerman, P.J., Cameron, D.G. & Riveros, F., 1988. Tropical forage legumes. 2nd Edition. FAO Plant Production and Protection Series No 2. Food and Agriculture Organization of the United Nations, Rome, Italy. pp. 464-465.
• Tateishi, Y. & Nackejima, C., 1990. The place of origin of Vigna hosei (Leguminosae) naturalized in Okinawa Island, the Ryukyu Islands. Journal of Japanese Botany 65: 243-247.

Authors

• K.C. Wong