Stylosanthes guianensis (PROSEA)
Stylosanthes guianensis (Aublet) Swartz
- Protologue: Svenska Vet. Akad. Handl. 10: 301 (1789).
- Family: Leguminosae
- Chromosome number: 2n= 20
Trifolium guianense Aublet (1775).
- Stylo, Brazilian lucerne (En). Luzerne du Brésil, luzerne tropicale (Fr)
- Thailand: thua-satailo.
Origin and geographic distribution
The natural distribution of stylo ranges from northern Argentina into Mexico. The variety guianensis, which is of particular interest to South-East Asia, has its centre of origin in Brazil and is naturally distributed to Paraguay, Bolivia, Peru, Colombia, Venezuela, Guyana and Central America. During the 20th Century it has been introduced all over the tropical world and is now widely naturalized in most tropical countries.
Stylo is used as a cover crop in plantations, as a green manure crop and as a fallow crop in shifting cultivation, but it is best known as a pasture legume for humid tropical regions.
Nitrogen concentrations range from 1.5-3.0%. Dry matter digestibility of young plant material lies between 60% and 70%, but with increasing age and lignification this may be reduced to below 40%. Because stylo is able to grow on poor soil, its P concentration is often as low as 0.06%, but with P fertilization it can increase to over 0.30% of DM. Stylo can grow adequately on soils with a low phosphate availability, in which case animals feeding on the plant need to be supplemented with P for their normal requirements. Although stylo is readily eaten by cattle and sheep, its palatability is not very high, which protects it from being overgrazed. As with many other tropical legumes, young growth of stylo is less palatable than young growth of grasses.
A perennial herb or sub-shrub, semi-erect to erect, with a strong taproot and small round root nodules. Stem much branched, herbaceous or lignified at the base, to 1 m tall, indumentum varying from nearly glabrous to densely pilose, often with bristles and viscid. Leaves trifoliolate; petiole 1-12 mm, rachis 0.5-1.5 mm long; stipules 2-15 mm, adnate to the petiole, teeth 2-10 mm long; leaflets elliptical to lanceolate, 5-45 mm × 2-20 mm, not more than 8 times longer than wide, indumentum varying as on stems. Inflorescence a loosely capitate spike, terminal or axillary, with more than 4 flowers. Flower subtended by an outer bract with 3-7 mm long sheath, a 2.5-5.5 mm long outer bracteole and a 2-4.5 mm long inner bracteole; calyx tube 4-8 mm long, lobes 3-5 mm; standard 4-8 mm × 3-5 mm, yellow to orange, often with black stripes, wings and keel 3.5-5 mm long. Pod usually 1-jointed, the article ovoid, 2-3 mm × 1.5-2.5 mm, glabrous or rarely with very short pubescence, indistinctly veined, with a minute beak, strongly inflexed. Seeds pale brown or purple.
Growth and development
Stylo plants have a juvenile phase during which floral initiation does not take place. Stylo is a copious seed producer, but more than 70% may be hardseeded. Hardseededness breaks down naturally under hot conditions and can also be broken by dry or wet heat before sowing.
As it fixes atmospheric N, stylo contributes to increased soil fertility, although it has been compared unfavourably with other legumes in this respect. It nodulates freely with cowpea rhizobia and does not require inoculation.
Other botanical information
In S. guianensis 7 varieties are distinguished by morphological and ecological characteristics. Only var. guianensis is important for South-East Asia and the information given here refers mainly to this variety. Another variety adapted for humid tropical regions is var. gracilis (Kunth) J. Vogel (syn. S. gracilis Kunth), but this has no agronomic value. Several cultivars of var. guianensis have been developed in Australia and South America. The cultivars released in Australia are : "Schofield", adapted to hot humid climates; "Cook", similar to "Schofield" but earlier flowering, more branched and better adapted to lower temperatures; "Endeavour" intermediate between cultivars "Schofield" and "Cook"; "Graham", the earliest flowering cultivar and better adapted to subtropical conditions. "Pucallpa", released in Peru specifically for the humid tropics and soils with a low pH. This cultivar is also widely used in tropical China as "Pi Hua Dou 184". Var. intermedia (Vogel) Hassler "Oxley" (known as fine stem stylo) is adapted to subtropical sub-humid regions with 700-1000 mm annual rainfall and is frost-tolerant.
The name S. guianensis is sometimes erroneously spelled S. guyanensis .
Stylo is adapted to hot, humid climates, and is neither frost nor drought tolerant. It grows on all soil types, but is particularly well adapted to poor acid soils with high Al and Mn contents.
Stylo is a short-day plant with a critical photoperiod of between 12-14 hours, depending on cultivar. However, some cultivars have been reported to require exposure to long days prior to short days before flowering is initiated. Cultivars with a critical photoperiod about 12 hours will only flower sporadically at the equator because of daylength requirements.
Propagation and planting
Stylo is propagated by seed. Hot water treatment (10 minutes at 80 °C) to break hardseededness improves germination rates. Seeding rate is 2-6 kg/ha. When sown together with grasses a good seed-bed preparation is desirable, but when sown into an existing pasture, little or no seed-bed preparation is necessary although establishment will be slower. Stylo can also be grown in a pure stand as a green manure, cover or fodder crop. It is suitable for small- and large-scale agriculture.
Stylo can be used by continuous or rotational grazing or cutting. It responds to improved soil fertility, particularly P, but can grow on infertile soil.
It is sometimes sown as a pioneer species in a mixture of legume species. In this role, it provides forage early in the life of the pasture, but is not expected to persist in the long term.
Diseases and pests
Stylo is susceptible to anthracnose disease, caused by the fungi Colletotrichum gloeosporioides and C. dematium, the former being the more important one. The disease was first reported from Brazil, but has now spread throughout the world by transport of infected seed. Symptoms of the infection are black lesions on the leaves and stems, which eventually lead to the death of the plants. Although the fungi can be controlled chemically, this is not an economic proposition, except for valuable seed crops. The approach being followed in Australia and Colombia is to select resistant cultivars. It has been reported by CIAT (Colombia), that stylo is more resistant to the disease in humid than in seasonally dry tropical regions, because of the presence of microorganisms antagonistic to the fungi.
Stylo is harvested by grazing animals or it is mown for stall feeding or artificial drying. When mown, care should be taken not to cut woody stems too low, otherwise regrowth will be adversely affected. Although usually consumed fresh, the forage can also be artificially dried. Hay making or ensiling are not commonly practised in the humid tropics.
In pure stands stylo can produce DM up to 10 t/ha and its contribution in mixed pastures can amount to 2-6 t/ha, depending on soil fertility and moisture level.
Cattle liveweight gains of 140 kg/animal and 400 kg/ha were recorded in Peninsular Malaysia in the third year of continuous grazing of a guinea grass ( Panicum maximum Jacq.) pasture containing 18% stylo and 7% centro ( Centrosema pubescens Benth.).
Stylo is well represented in South-East Asia and seed is on sale. Germplasm collections are available at ATFGRC (CSIRO, Australia) and CIAT (Colombia).
Plant breeding programmes are in progress in Queensland, Australia, for anthracnose resistance within var. intermedia . The available natural variation within the species allows selection for adapted cultivars to a wide range of environmental conditions. Plant collections in South America also offer scope for further cultivar development and improvement.
It is unlikely that much effort will be put into improving the adaptation or yield of S. guianensis, because there are other species of Stylosanthes that can take its place.
- Burt, R.L., Cameron, D.G., Cameron, D.F., 't Mannetje, L. & Lenné, J.M., 1983. Stylosanthes. 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. 141-181.
- Skerman, P.J., Cameron, D.G. & Riveros, F., 1988. Tropical forage legumes. FAO, Rome. pp. 394-407.
- Stace, H.M. & Edye, L.A. (Editors), 1984. The biology and agronomy of Stylosanthes. Academic Press, Sydney, Australia. 636 pp.
- 't Mannetje, L., 1977. A revision of varieties of Stylosanthes guianensis (Aubl.) Sw. Australian Journal of Botany 25: 347-362.
L. 't Mannetje