Stylosanthes humilis (PROSEA)
Stylosanthes humilis Kunth
- Protologue: Nov. gen. sp. 6: 506, t. 594 (1824).
- Family: Leguminosae
- Chromosome number: 2n= 20
S. figueroae Mohl. (1957).
- Townsville stylo, Townsville lucerne (En)
- Philippines: magsaysay-lucerne (Tagalog)
- Thailand: thua-satailo.
Origin and geographic distribution
Townsville stylo is widespread in Brazil and also occurs in Venezuela, Colombia, Central America, Mexico and Cuba. It is adventive to Queensland (Australia) and is naturalized in Malaysia, Indonesia and Thailand.
Townsville stylo is a forage particularly useful in heavily grazed areas in the semi-arid to subhumid tropical and lower latitude subtropical regions with a marked dry season.
The N and P concentrations of whole plants range from 3.0-1.6% and 0.20-0.04% respectively. The DM digestibility of young plant material lies between 60% and 70%, but with increasing age it is reduced to 40%. Seed has a DM digestibility of ca. 62%. There are 275-300 seeds/g with pods and 400-500 seeds/g without pods.
A herbaceous, usually erect but sometimes prostrate annual, 0.5 m tall, branched, usually with short white hairs along one side of the stem and often with scattered short bristles on the stem and nodes. Leaves trifoliolate; leaflets lanceolate or sometimes elliptical, acute, both surfaces nearly glabrous, with 3-6 pairs of conspicuous veins; terminal leaflet up to 15 mm × 3.5 mm; petioles 3-5 mm long, shortly hairy and often with scattered bristles; stipules bidentate, adnate to base of petiole with bristles on both sheath and teeth. Inflorescence consists of several short, ovoid, crowded spikes with 5-15 flowers in each spike; spikes hirsute without axis rudiment; flower with one inner and one outer bracteole; calyx tube 4-5 mm long, lobes 1.5 mm long; corolla bright yellow; standard 3-4 mm × 3-4 mm. Fruit a loment, 1.5-2.5 mm broad, reticulately nerved; only the upper articulation fertile, 1.5-2.5 mm long, with beak 4-10 mm long; beak 1.5-3 times the length of the upper articulation and strongly uncinate to coiled. Seed yellowish-brown.
Growth and development
Embryo dormancy is high with up to 94% in July in northern Australia at the end of the wet season, but is short lived and has disappeared by October. Hard-seededness can be as high as 100% in July but it breaks down rapidly to 1-6% by December when maximum diurnal soil temperatures are 50-55 °C under field conditions. Hard-seed breakdown occurs to a lesser extent when the soil surface is moist as the temperatures do not rise above 40 °C. It germinates freely following early summer rain and the seedlings are able to withstand considerable water stress and then grow rapidly during the vegetative and early reproductive stage if the soil moisture is adequate. It has a short-day flowering response with a critical photoperiod of 12-14 hours. It nodulates freely with the cowpea type rhizobia and does not require inoculation. Once Townsville stylo plants become established the major influences on growth are water, nutrition and amount of competition from associated grasses. Flowering is genetically controlled with shorter critical photoperiod flowering being dominant. Flowering occurs over 8-10 weeks and seed ripens over a similar time interval. It avoids long dry seasons as predominantly hard-seed.
Other botanical information
Collections of Townsville stylo can be divided into two major groups. One includes adventive populations from Australia, Colombia, Dominican Republic, Ivory Coast, Kenya, the Philippines, Tanzania, the United States, as well as collections from Brazil of supposedly indigenous material. The second group includes collections from Venezuela, Costa Rica, Nicaragua and Mexico. The evidence suggests that Townsville stylo is not native to Brazil and that it first occurred around ports in north-eastern Brazil in the late 19th Century about the same time as its first recorded occurrence in Australia.
The cultivars released in Queensland, Australia during the late 1960's were the common naturalized type, "Paterson" (early flowering), "Lawson" (mid season flowering) and "Gordon" (late flowering). All the Australian naturalized populations and cultivars proved highly susceptible to the fungal disease anthracnose when it was accidentally introduced into Australia ca. 1973.
Townsville stylo's adaptation in Australia to a wide latitudinal range (12-28°S) with annual rainfall ranging from 600-1500 mm is due to ecotypic variation in critical photoperiod. Rainfall and latitude delineate ecotypic occurrences; ecotypes with a long critical photoperiod are restricted to drier or higher latitude regions whilst those with a shorter critical photoperiod are adapted to higher rainfall regions at lower latitudes. Although it will persist in regions with as little as 600 mm annual rainfall, it is not sufficiently productive to enhance animal production below 800 mm rainfall. It occurs on infertile sandy to clay loam soils with a pH(H2O) range of 5 to 6.5. It is unsuited to heavier textured and more fertile soils, including cracking clays and soils derived from basalt or other igneous rocks, and also saline coastal soils.
Townsville stylo is sensitive to shading when grown in mixtures with taller grasses.
Propagation and planting
Townsville stylo is propagated by seed. Hard-seededness can be broken by mechanical scarification or hot water or dry heat treatment. Seeding rate is 2-3 kg/ha. In semi-arid environments, seed can be surface sown onto existing pastures following burning just prior to the expected start of the wet season.
In Thailand, the anthracnose-resistant cultivar "Khon Kaen" was released in 1984 because it showed greater productivity and persistence than S. hamata (L.) Taub. "Verano" under extremely heavy grazing, because of its prostrate growth habit. It is oversown onto communal grazing lands which are subjected to very heavy continuous grazing. Townsville stylo was widely used for pasture improvement in northern Australia during 1960-1974 but, since the advent of anthracnose it is of little importance as it has been superseded by the anthracnose-resistant cultivars of S. hamata , "Verano" and "Amiga", and of S. scabra Vogel "Seca" and "Siran".
Diseases and pests
Townsville stylo is susceptible 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 Townsville stylo (e.g. "Khon Kaen"). Blight ( Sclerotium rolfsii ) and bacterial wilt ( Pseudomonas solanacearum ) have been recorded on Townsville stylo in Australia. There are no known important insect pests.
Although usually consumed fresh by grazing animals, Townsville stylo can be cut and fed when grown or made into hay towards the end of the growing season. Prior to the advent of anthracnose, feeding of Townsville stylo hay during the dry season was commonly practised in northern Australia to encourage seed dispersal by cattle.
Townsville stylo has a high seed yield potential up to 1250 kg/ha and actual machine harvested yields of 600 kg/ha. Yields of dry matter can range from 1-6 t/ha.
Major germplasm collections are held by ATFGRC (CSIRO, Australia) and CIAT (Columbia).
There are no plant breeding programmes in progress.
It is unlikely that any effort will be put into improving adaptation and yield of S. humilis because there are other Stylosanthes species that can take its place.
- 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.
- Gillard, P. & Fisher, M.J., 1978. The ecology of Townsville stylo-based pastures in northern Australia. In: Wilson, J.R. (Editor): Plant relations in pastures. CSIRO, Melbourne. pp. 340-352
- Shaw, N.H. & 't Mannetje, L., 1970. Studies on a spear grass pasture in central coastal Queensland - the effect of fertilizer, stocking rate, and oversowing with Stylosanthes humilis on leaf production and botanical composition. Tropical Grasslands 4: 43-56.
- Stace, H.M. & Edye, L.A. (Editors), 1984. The biology and agronomy of Stylosanthes. Academic Press, Sydney. 636 pp.
L.A. Edye & A. Topark-Ngarm