Desmodium intortum (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Desmodium intortum (Miller) Urban

Protologue: Symb. Antill. 8: 292 (1920).

Family: Leguminosae

Chromosome number: 2n= 22

Synonyms

Hedysarum intortum Miller (1768), Desmodium aparines (Link) DC. (1825).

Vernacular names

• Greenleaf desmodium (En). Pega-pega (Sp)
• Philippines: karikut-ritkut (Bagobo)
• Thailand: thua kleen leap.

Origin and geographic distribution

Greenleaf desmodium is native to the Americas, from southern Mexico to as far south as southern Brazil. Following widespread testing as a forage legume, it is now naturalized in small areas of the higher rainfall subtropics and elevated tropics. In Souht-East Asia it occurs most in Papua New Guinea, the Philippines and Thailand.

Uses

Greenleaf desmodium is mostly utilized as a pasture legume in mixed sowings with grasses. It can also be cut for use as fresh fodder or for hay or made into silage.

Properties

Nitrogen concentrations in top growth range from 2-4.2%. In one sampling the N concentration in leaves (3.7%) was double that of the stems (1.7%). Phosphorus concentrations in leaf material range from 0.10-0.45%. Tannin levels in leaves range from 3-9% which may account for the somewhat low in vitro digestibility range of 55-60%.

Botany

A robust taprooted perennial herb with trailing stems and stolons to several metres long. Stems form roots if in contact with moist soil and may scramble, but not twine, over the surrounding vegetation; they are grooved, often reddish in colour, densely covered with short hooked hairs, glandular, sticky to the touch. Leaves with three leaflets; petiole up to 5 cm long; leaflets usually ovate, 3-12 cm × 1.5-7 cm, the lateral ones smaller than the terminal, often with sparse reddish-brown marks on the upper surface, covered with ascending hairs on both surfaces. Inflorescence a quite dense terminal or axillary panicle up to 30 cm long; flowers pink to purple, 8 mm long, borne in pairs within the axils of caducous bracts. Pod 15-50 mm × 3-4 mm, curved, up to 12-articulate, covered with short hooked hairs and hence adhering to animals and clothing, slightly indented along the upper margin, more strongly indented along the lower margin between the 3-7 mm long articles, breaking up at maturity. Seed reniform, 2 mm × 1.3 mm.

D. intortum is closely related to D. uncinatum (Jacq.) DC., together forming a complex which is taxonomically not well separated and in which more names are involved (e.g. D. aparines (Link) DC.).

Greenleaf desmodium is self fertile but flowers may require tripping for pollination to occur. Seedlings develop slowly and require favourable conditions during the first weeks of growth.

Once established, greenleaf desmodium makes vigorous growth. In the higher latitude tropics and in the subtropics it has a long growing season before flowering late in the wet season. It does not spread readily from seed but individual plants can spread quite a long distance by means of stolons. Well-known cultivars are "Greenleaf" (Australia) and "Tengeru" (Tanzania).

Ecology

Greenleaf desmodium usually requires more than 1100 mm annual rainfall. It can be grown at sea-level in the subtropics, but favours elevated areas (500-2000 m) in the tropics. Hence it has shown promise in the wetter Australian subtropics and in elevated tropical areas as in Papua New Guinea, Thailand and the Philippines. It is tolerant of shade, but not adapted to the lowland tropics where the major plantation crops are grown. It is susceptible to heavy frosts and also to extended dry spells during the growing season. It will grow satisfactorily on a range of soils, from sandy soils to clay loams, provided the pH(H₂O) is not less than 5.0 (preferably 5.5) and they are not saline. It is intolerant of fire.

Agronomy

"Greenleaf" is sown by seed into a well-prepared seed-bed, or more rarely established by rooted cuttings. Seed may be drilled to a depth not exceeding 10 mm, or broadcast; seeding rates are generally 1-2 kg/ha. It does not establish satisfactorily when oversown into an existing pasture. Mechanically-harvested seed exhibits negligible hard-seededness, but hand-harvested seed may benefit from treatment with sulphuric acid for five minutes, followed by washing. Seed should be inoculated with a specific "desmodium" culture of Bradyrhizobium. It is generally sown with a companion grass such as Setaria sphacelata (Schumacher) Stapf & C.E. Hubbard ex M.B. Moss and sometimes together with other tropical pasture legumes. Greenleaf desmodium requires moderate to high levels of P, S, K and Mo for growth. It has a higher requirement for Mo than most tropical legumes.

Several fungal diseases have been reported on greenleaf desmodium but usually they have had minimal impact on persistence and production. Little leaf, caused by a mycoplasma-like organism also occurs but usually only affects isolated plants. In Australia, the most important pests are weevil larvae of Amnemus and Leptopius spp. which damage or even sever taproots and larger adventitious roots, making "Greenleaf" more susceptible to soil moisture stress.

It will usually be eliminated from a pasture by frequent close cutting or heavy grazing, as this removes axillary and terminal buds and reduces the plant's ability to recover. Even with appropriate grazing management and a suitable environment, "Greenleaf" may only persist for 5-10 years.

"Greenleaf" is usually grazed by cattle, although it can be used in a cut-and-carry system. Annual DM yields of 12-19 t/ha have been recorded from "Greenleaf" grown in pure stands or in mixtures with grasses. Liveweight gains from "Greenleaf"/grass pastures usually range from 250-600 kg/ha per year, although higher gains have also been recorded. Given low grazing pressure, liveweight gains of over 200 kg/head per year can be obtained from good "Greenleaf" pastures. Milk production from Jersey cows grazing pure "Greenleaf" was only 7.7 kg/day. This may have been associated with difficulties in achieving a high intake from the open sward; higher milk production figures have been obtained from "Greenleaf"/grass pastures.

Genetic resources and breeding

Germplasm collections are available at ATFGRC (CSIRO, Australia) and CIAT (Columbia). There is little variation within the species in most agronomic characters, but there is variation in resistance to nematodes. This suggests that, where this is a problem, genetic advances can be made. Breeding in Australia to improve seedling vigour, by hybridization with the related D. sandwicense E. Meyer and selection for large seed size, was discontinued.

Prospects

Greenleaf desmodium has a restricted range of adaptation and will be further restricted by its inability to withstand sustained heavy cutting or grazing. However, within the limited areas and farm systems to which it is suited, it is a productive legume.

Literature

• Bogdan, A.V., 1977. Tropical pasture and fodder plants. Longman, London. pp. 344-348.
• Imrie, B.C., Jones, R.M. & Kerridge, P.C., 1983. Desmodium. In: Burt, R.L., Rotar, P.P., Walker, J.L. & Silvey, M.W. (Editors): The role of Centrosema, Desmodium and Stylosanthes in improving tropical pastures. Westview Press, Boulder, Colorado, United States. pp. 97-140.
• Jones, R.M., 1989. Productivity and population dynamics of silverleaf desmodium (Desmodium uncinatum) and greenleaf desmodium (Desmodium intortum) and two D. intortum × D. sandwicense hybrids at two stocking rates in coastal south-east Queensland. Tropical Grasslands 23: 43-55.
• Lenné, J.M. & Stanton, J.M., 1990. Diseases of Desmodium species. Tropical Grasslands 24: 1-14.
• Skerman, P.J., Cameron, D.G. & Riveros, F., 1988. Tropical forage legumes. FAO, Rome. pp. 274-282.

Authors

J.B. Hacker