Stylosanthes hamata (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Stylosanthes hamata (L.) Taub.

Protologue: Verh. Bot. Ver. Brandenb. 32: 22 (1890).

Family: Leguminosae

Chromosome number: 2n= 20, 40

Synonyms

Hedysarum hamatum L. (1759), Stylosanthes procumbens Swartz (1788).

Vernacular names

• Caribbean stylo (En)
• Laos: hnha:z liaz ngu:
• Thailand: thua-hamata.

Origin and geographic distribution

S. hamata is indigenous to the drier habitats of the Caribbean Islands, southern Florida, Central America and South America. In South America it is recorded from Colombia, Venezuela and Brazil (Ceara, Pernambuco and Bahia). Tetraploid as well as diploid races occur in Central and South America but tetraploids have not been recorded in the Caribbean Islands or Florida.

Uses

The tetraploid Caribbean stylo cultivars "Verano" and "Amiga" are widely used as a pasture legume in northern Australia, Thailand, India, Nigeria and other West African countries. It can also be cut and fed fresh or used to make hay. Diploid S. hamata accessions have so far not been used as sown pasture legumes.

Properties

The N and P concentrations of whole plants of Caribbean stylo sampled at flowering averaged 1.8% and 0.08%, respectively. The DM digestibility and DM intake of young plant material grown under irrigation with P fertilizer averaged 80% and 73 g/kg Lw^0.75when fed to sheep. The N and P concentrations and in vitro digestibility (IVD) of leaf and stem fractions generally differ from each other and decline during the growing season. In green leaves, the mean N concentration falls from 3.9% to 2.7%, P concentration from 0.37% to 0.16% and IVD from 72% to 66%. In stems, the corresponding changes were 2.0% to 1.0% N, 0.34% to 0.06% P and 57% to 33% IVD. However, P levels will vary with soil P status. The IVD of inflorescence and seed is 69% and 60% respectively.

There are about 270 seeds/g with pods and 450 seeds/g without pods.

Description

The tetraploid is a short-lived perennial herb, usually with an erect habit but sometimes prostrate, 0.5 m or more tall, with much branched stems; internodes 2-8 cm long, line of ascending whitish indumentum changing sides on successive internodes, glabrous elsewhere. Leaves trifoliolate; leaflets narrowly elliptical-lanceolate, central leaflet 16-26 mm × 3-6 mm, acute at base and tip, mucronate, sparsely hairy above and below, central vein prominent below, 4-6 pairs lateral whitish veins, margins entire or minutely denticulate at base of whitish hairs; petioles 3-6 mm long, grooved with 2 lines of hairs; stipules bidentate, adnate to the base of the petiole with hairs on the sheath and teeth; sheath about 6 mm long. Inflorescence axillary or terminal, indeterminate, with 8-14 flowers; terminal inflorescence with 2-3 alternate spikes; outer bracts trifoliate, broader than stipules but venation and pilosity similar; inner bracts unifoliate, evenly sericeous; corolla tube 3 mm long; standard petal 4-5 mm wide, yellow with reddish mark; wings and keel petals yellow; axis rudiment 4-5 mm long in first flower of the spike, 1-2 mm in the next flower, minute or absent in upper flowers; there are two inner bracteoles. Fruit a loment, usually with two fertile articles, upper article 6-7 mm long including distally recurved beak 3-4 mm long, body with prominent nerve on each side, reticulate, minute hairs on edges; lower article 3.5 mm long with dense white hairs. Seeds 2.5 mm × 1.5 mm, tan to dark maroon, mottled.

Growth and development

Embryo dormancy of tetraploid S. hamata is high with up to 50% in July at the end of the wet season in Queensland, Australia and has disappeared by October. Hard-seededness (> 97%) occurs where the mean temperature during seed formation is above 24 °C but is less at lower temperature (64% at 21 °C and 30% at 20/16 °C). Seed germinates freely following early summer rain and the seedlings are able to withstand considerable water stress. It flowers 9-10 weeks after germination, and plants will flower within 6 weeks of the start of the season. Seed ripens over a period of 15-16 days after flowering. It largely behaves as an annual except in the second year when the survival rate of first-year plants can be as high as 93%. It avoids long dry seasons as predominantly hard seed which rapidly breaks down when the maximum diurnal soil temperatures reach 50-55 °C just before the onset of the wet season.

The tetraploid S. hamata lines have an indeterminate flowering response to short days.

Other botanical information

Strictly S. hamata refers to the diploid species and the tetraploids may be a separate species. There is genetic evidence that the tetraploids have evolved as an allotetraploid combination of S. hamata (2 n = 20) and S. humilis Kunth (2 n = 20); both diploid species are sympatric or nearly so with the tetraploids.

Because the tetraploid S. hamata (2 n = 40) is largely sympatrical with its diploid progenitors S. hamata and S. humilis , it is advantageous to distinguish between them. The tetraploid and diploid S. hamata have similarities in the presence of a fine line of indumentum on one side of each internode, the presence of an axis rudiment, the loment often with two fertile articles and the absence of bristles on stems. The tetraploid differs from the diploid in its short-lived perenniality, the axis rudiment present in the lower flowers only, the presence of a long terminal bristle on the tips of the stipules and bracts, and in its darker coloured and longer seed. Although the tetraploid S. hamata is superficially similar to S. humilis, the latter differs from the tetraploid in having abundant bristles on stems, stipules and bracts; stipules forming a fused sheath around the stem; the loment with only one fertile article; no axis rudiment and is an obligate annual.

Cultivars "Verano" and "Amiga" were released in Queensland in 1973 and 1988 respectively. Although both cultivars are morphologically similar, they differ in that "Amiga" gives 40-50% higher seed yields and appears better adapted to high altitude (> 300 m) environments than "Verano".

Ecology

Tetraploid Caribbean stylo is suited to semi-arid to sub-humid tropical regions with short variable growing seasons and an annual rainfall of 500-2000 mm. It is poorly adapted to subtropical environments. It grows on a wide variety of soil types ranging from sands to clay loams, but not on heavy clays. It is particularly well adapted to infertile, moderately acid and sandy surface soils with very low P levels. This adaptation is enhanced by its efficiency in extracting less available forms of soil P. The diploid Caribbean stylo occurs on neutral to slightly alkaline soils and is less adapted to acid conditions.

Propagation and planting

Caribbean stylo is propagated by seed. Hard-seededness can be broken by mechanical scarification or hot water treatment to improve germination. Seeding rate is usually 2-3 kg/ha. In drier regions it should be sown with S. scabra Vog. cultivars "Seca" and/or "Siran" at 1 kg/ha and in the wetter areas other legumes such as Aeschynomene americana L. "Glen" and Stylosanthes guianensis (Aublet) Swartz "Cook" could be included in the mixture. In semi-arid environments the seed can be surface sown onto existing pasture following burning. When sown together with improved grasses, usually in more humid environments, a well prepared seed-bed is desirable. The tetraploid cultivars nodulate freely with the native cowpea rhizobia and do not require inoculation. Caribbean stylo pastures require early grazing soon after establishment to reduce the competition from grasses as Caribbean stylo is less palatable than the young growth of grasses.

Husbandry

Caribbean stylo can be utilized by continuous or rotational grazing or cutting. Because it can grow at very low P levels, it may be necessary to apply 10 to 20 kg/ha of P at establishment and periodically thereafter to maintain soil P at 8 mg/kg so that the P concentration in the herbage reaches a level of above 0.12% during the growing season to insure adequate animal nutrition. Alternatively, grazing animals can be directly supplemented with P to meet their dietary requirements.

Diseases and pests

Caribbean stylo is largely resistant to anthracnose disease caused by the fungi Colletotrichum gloeosporioides and C. dematium (see S. guianensis ). There is some variation in anthracnose resistance between naturally occurring genotypes of Caribbean stylo; "Verano" and "Amiga" show a high field resistance to anthracnose. Web blight ( Rhizoctonia solani ) can damage vegetative growth of Caribbean stylo during the wet season in Queensland and head blight ( Botrytis cinerea ) can cause yield losses in seed crops. The latter fungus causes extensive blossom blighting and apical dieback. Under wet conditions conducive to disease development a grey-coloured mould grows over the inflorescences. There are no important insect pests of Caribbean stylo.

Harvesting

Caribbean stylo is usually harvested by grazing animals but can be cut for stall feeding as green feed or to make hay. Caribbean stylo paddocks that are cut may need resting from cutting every third or fourth year to allow seed reserves to build up.

Yield

In pure stands, Caribbean stylo can produce up to 10 t/ha of DM in high rainfall environments with adequate fertilizer. Its contribution in mixed pastures usually ranges from 1-7 t/ha depending on soil fertility, moisture level and the competition from grasses. Heavy grazing encourages legume dominance in mixed Caribbean stylo-grass pastures. Tetrapolid S. hamata lines have a high seed potential from 1750-2000 kg/ha. Actual machine harvester yields can reach 1000 kg/ha. Annual liveweight gains of 140 to 160 kg/head have been recorded from Caribbean stylo-shrubby stylo pastures on lightly fertilized poor soils in northern Queensland.

Genetic resources

Germplasm collections are maintained by ATFGRC (CSIRO, Australia) and CIAT (Colombia).

Breeding

Plant breeding programmes are in progress in Queensland, Australia, to develop cultivars with greater anthracnose resistance than "Verano" and "Amiga". Accessions with low disease damage could have potential as parents for a breeding programme to improve anthracnose resistance and in studies of the genetics of anthracnose resistance.

Prospects

The wide range of adaptation and productivity of Caribbean stylos will encourage further plant improvement programmes through plant breeding and the selection of naturally occurring genotypes. Besides resistance to anthracnose, other desirable objectives are increased seed yield and colonizing ability. It is well suited to the drier parts of South-East Asia.

Literature

• Edye, L.A., Burt, R.L., Nicholson, C.H.L., Williams, R.J. & Williams, W.T., 1974. Classification of the Stylosanthes collection 1928-1969. CSIRO, Australia, Division of Tropical Agronomy Technical Paper No 15. 28 pp.
• Edye, L.A., Hall, T.J., Middleton, C.H., Messer, W.B., Piggin, C.M., Schlink, A.C. & Klepacki, N.M., 1991. Sward evaluation of fifteen Stylosanthes hamata accessions in twenty dry tropical environments. Tropical Grasslands 25: 1-11.
• Oram, R.N., 1990. Register of Australian herbage plant cultivars. CSIRO, Australia. pp. 256-257.
• Stace, H.M. & Cameron, D.F., 1987. Cytogenetic review of taxa in Stylosanthes hamata sensu lato. Tropical Grasslands 21: 182-188.
• Stace, H.M. & Edye, L.A. (Editors), 1984. The biology and agronomy of Stylosanthes. Academic Press, Sydney, Australia. 636 pp.

Authors

L.A. Edye & A. Topark-Ngarm