Centrosema pascuorum (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Centrosema pascuorum Martius ex Benth.

Protologue: Comm. legum. gen.: 56 (1837).

Family: Leguminosae

Chromosome number: 2n= 22

• Centurion (Australia) (En).

The origin and natural distribution of this species is in tropical South and Central America, mainly in semi-arid regions in north-eastern Brazil, Venezuela, Guyana, Ecuador, Panama, Costa Rica, Honduras, Guatemala and southern Mexico. C. pascuorum also occurs naturally in the Brazilian Pantanal. It has been introduced recently to Australia (Northern Territory and Queensland) and to most countries in South-East Asia, including Indonesia, Malaysia, the Philippines and Papua New Guinea.

C. pascuorum is sown as a pasture legume in northern Australia, mainly in regions with a long dry, but reliable wet season, or in seasonally flooded parts of the Northern Territory. It is sometimes cut for hay. It has been planted experimentally in South-East Asia.

C. pascuorum is regarded as a relatively palatable, high quality tropical forage. Nitrogen concentrations range from 2.5-4.3%. In vitro DM digestibility of young plant material has been measured at 64%, and P concentrations varies from 0.15-0.18%. There are 48-58 seeds/g in the two Australian cultivars.

An annual, herbaceous plant with a twining or scrambling habit, producing roots on trailing stems in moist conditions. Stem cylindrical, glabrous to scarcely pilose, branched at the nodes, up to 2 m long. Leaf trifoliolate and often held erect; stipules narrowly triangular, 4-9 mm long; petiole 1.7-5 cm long including the upper rachis; leaflets long and narrow, 2-15 cm × 0.3-1.7 cm, glabrous to scarcely pilose, with acute to acuminate apices. Inflorescence racemose, with 1-2 peduncles per leaf axil; flower resupinate, singly or in pairs at the end of a short (0.5-2 cm) peduncle; pedicel 4-10 mm long, subtended by a single ovate bract 2-4 mm long with at the distal end two conspicuously paired bracteoles which are ovate, 4-6 mm × 2-4 mm, with acuminate apices; calyx tube 3-4 mm long, with 5 narrow teeth 3-7 mm in length; the lowest tooth (4-7 mm) is the longest; corolla wine red, 15-25 mm long and wide; the standard with a spur on the back towards the base. Pod linear, 4-8 cm × 3-4 mm, laterally compressed, with a dark longitudinal stripe near each suture, containing up to 15 seeds; the pod shatters at maturity. Seed ovoid to cylindrical, ca. 4 mm long, slightly compressed laterally, greenish-yellow to brown, rarely mottled (accessions from Venezuela).

Minute hooked hairs occur on the outer surfaces of the calyx, bracts and bracteoles, and more sparsely on the leaves and stems.

Photoperiod and temperature influence flowering and seed production. In cultivar "Cavalcade", flowering occurs in short days (12 hour photoperiod or less). In longer days (13 hour photoperiod) buds may be produced, but they abort at high temperatures (33/28 °C day/night) and no seeds are produced. Soil seed reserves of 250 kg/ha are common in good pastures. Hard seed content is high (90-100%) when seeds ripen, but declines to 10-30% at the end of the dry season.

Two botanical varieties of C. pascuorum have been named, but neither is widely recognized. Ecotypes from Ecuador often have larger leaves and seeds, and paler flowers, than those from elsewhere. Ecotypes from Venezuela have smaller, mottled seeds. Accessions from north-eastern Brazil are more diverse and usually more vigorous than those from elsewhere. A few accessions from Brazil and Venezuela have ovate leaflets. Two cultivars, "Cavalcade" and "Bundey", have been released in Australia.

C. pascuorum is adapted to tropical regions having reliable wet (4-6 months, 700-1500 mm) and dry seasons. It is drought resistant, but can also survive prolonged waterlogging or flooding (partial immersion). It will not persist in the subtropics and is not frost-tolerant. It is adapted to soils of near-neutral pH, ranging from sand to heavy clay.

C. pascuorum is propagated by seed, at a seeding rate of 2-5 kg/ha. Heat treatment to reduce hard-seededness may be necessary for hand-harvested seed. Inoculation of seed with an appropriate strain of Bradyrhizobium is advised, but is usually not essential. A cultivated seed-bed is required, and the seed should be covered with soil to a depth of 1-2 cm. Seed should be planted at the start of the wet season. Control of existing weeds and grasses during establishment is helpful. Grasses such as Cenchrus ciliaris L., Urochloa mosambicensis (Hack.) Dandy and Andropogon gayanus Kunth can be planted with C. pascuorum .

Heavy applications of fertilizer are not required, but C. pascuorum will usually respond well to low rates of P (5 kg/ha). In pastures it is a valuable dry season forage, but it can be grazed throughout the year provided the stocking rate during the second half of the wet season is low enough to allow good seed production. In Australia, 2-3 steers/ha can be carried during the dry season on good pastures.

C. pascuorum is susceptible to the fungal pathogens Cercospora canescens (leaf-spot), Colletotrichum truncatum (anthracnose), Pseudocercospora bradburyae (leaf-spot), Rhizoctonia solani (foliar blight) and Neocosmospora vasinfecta. However, these diseases are usually not serious in areas where it is well-adapted. It is also susceptible to root-knot nematodes ( Meloidogyne spp.), and to sucking insects during seed production. Control by chemicals usually is not economic except for commercial seed production.

C. pascuorum is usually grazed, or is cut for hay.

Annual DM yields of 4-6 t/ha are obtained from legume-dominant pastures in the semi-arid tropics. In small plots, yields of up to 9 t/ha have been measured in Thailand. Under favourable conditions, large quantities of seed are produced, exceeding 1 t/ha in pure stands.

Representative germplasm collections (80 accessions) are held by ATFGRC (CSIRO, Australia) and by CIAT (Colombia).

There are no active plant improvement programmes at present. A breeding programme in Australia from 1976-1981 led to the release of "Cavalcade". The breeding objectives were seed and forage yield, and freedom from symptoms of nematode infestation. Small numbers of accessions have been tested in most South-East Asian countries, notably Thailand.

C. pascuorum has potential for wider use as a pasture or hay legume in semi-arid tropical regions. Its ability to tolerate both drought and prolonged waterlogging is unusual in legumes. However, its proven area of adaptation in Australia is limited, and its variable performance in trials in South-East Asia suggests that its use may be restricted to a few areas in the drier parts of the region.

• Clements, R.J., Winter, W.H. & Reid, R., 1984. Evaluation of some Centrosema species in small plots in northern Australia. Tropical Grasslands 18: 83-91.
• Nulik, J., Andrews, A. & Jacobsen, C.N., 1986. Evaluation of grass and legume species in swards in Nusa Tenggara. In: Annual report of the Forage Research Project. Balai Penelitian Ternak (Research Institute for Animal Production), Bogor, West Java, Indonesia. pp. 28-31.
• Oram, R.N., 1990. Register of Australian herbage plant cultivars. CSIRO, Australia. pp. 272-274.
• Schultze-Kraft, R. & Clements, R.J. (Editors), 1990. Centrosema: biology, agronomy and utilization. CIAT, Cali, Colombia. 667 pp.
• Skerman, P.J., Cameron, D.G. & Riveros, F., 1988. Tropical forage legumes. FAO, Rome. pp. 238-242.
• Stockwell, T.G.H., Clements, R.J., Calder, G.J. & Winter, W.H., 1986. Evaluation of bred lines of Centrosema pascuorum in small plots in north-west Australia. Tropical Grasslands 20: 65-69.

R.J. Clements