Setaria sphacelata (PROSEA)
Setaria sphacelata (Schumach.) Stapf & Hubbard ex M.B. Moss
- Protologue: Kew Bull. 1929: 195 (1929).
- Family: Gramineae
- Chromosome number: 2n= 18 (diploid), 36, 45, 54, 72, 90 (decaploid)
* var. sphacelata : Panicum sphacelatum Schumacher (1827);
- var. sericea (Stapf) W.D. Clayton: Setaria anceps Stapf (1930);
- var. splendida (Stapf) W.D. Clayton: Setaria splendida Stapf (1930).
- General: setaria (En).
- var. splendida : splendida, broadleafed setaria (En)
- Malaysia: sekoi
- Philippines: bunga-bunga
- Thailand: ya taiwan
- Vietnam: co duôi chó, co ro'm.
Origin and geographic distribution
Setaria originates from and is widely distributed in tropical and subtropical Africa. It also occurs in Yemen. The species was first brought into cultivation as a pasture plant in Kenya and has since been widely planted throughout the tropics and subtropics, especially in Africa, Asia and Australia. It has become naturalized in many of the countries to which it was introduced. In South-East Asia it is widely planted in Malaysia and Indonesia but is of only minor importance in Thailand.
Setaria is an important forage and is used under grazing and in cut-and-carry systems. The botanical variety splendida is reported to be one of the more commonly used species for cut-and-carry systems in Indonesia and Malaysia.
Nitrogen concentrations vary from over 3% in very young growth to under 1% in old growth. It is difficult to compare nutrient concentrations in different cultivars, as they flower at different times. Setaria has a higher moisture content than some other tropical grasses. In Australia accessions have been shown to differ quite widely in digestibility and a range of chemical components, especially Na. Setaria is a species which accumulates oxalate, especially when heavily fertilized with N. This is normally not a problem with ruminants, such as cattle, provided they have been allowed to become used to setaria, but it is a problem with horses, which develop a condition known as big-head ( Osteodystrophia fibrosa ). There are 1200-1900 seeds/g.
A tufted, or more rarely rhizomatous, perennial with more or less erect stems to 3 m tall. Young tillers are strongly flattened in commercial cultivars, with leaf-sheath prominently keeled and often red-pigmented, sometimes hairy. Culms vary in number of internodes and diameter, depending on variety and cultivar, few and narrow in "Nandi", up to 17 and 6-12 mm in diameter in var. splendida ; nodes hairless; the culms occasionally branching when grown in fertile soils to give multiple inflorescences. Leaf-blade 10-70 cm × 11-12 mm in var. sericea, up to 20 mm wide in var. splendida , hairless or with a few long hairs close to the junction with the sheath. Inflorescence an elongated cylindrical spike-like panicle 10-50 cm long, the spikelets borne in groups of 2 or 3 on short branches, each spikelet subtended by 5-15 stiff bristles varying in length and colour; spikelets 2.5-3 mm long, flat on the side of the lower glume, convex on the other, the lower glume about _, the upper _ the length of the spikelet; lower floret male or sterile, the upper floret bisexual, the palea and lemma hardened and enclosing the caryopsis when ripe.
Growth and development
Var. splendida is near-sterile, but seed of other varieties germinates reasonably readily in good conditions and establishes without difficulty. If the initial stand has a low plant density, setaria has the capacity to thicken up if allowed to produce a seed crop. Flowering is variable within most cultivars, with plants and tillers within a plant poorly synchronized. Furthermore, a single inflorescence takes from 1-7 weeks to complete flowering. Thus the earliest-formed spikelets may be ripe and shedding when the latest ones have only just flowered. This poor synchrony, together with abscission of the spikelet soon after ripening, is a major contributory factor to low seed production in this species. In subtropical climates, setaria generally produces two seed crops a year.
Other botanical information
The mainly African S. sphacelata is a polyploid complex, running from diploid to decaploid, with the different ploidy levels crossing freely without showing clearly different morphological characters. For convenience only, the enormous variability of the complex species has been divided into 5 botanical varieties which, however, intergrade completely and do not represent discrete entities. Only two varieties are in commercial use:
- var. sericea : culms 4-10-noded, 3-6 mm in diameter, up to 2 m tall; basal leaf-sheaths conspicuously flabellate; leaf-blades 3-10 mm wide, glabrous; panicle 7-25 cm long; bristles fulvous.
- var. splendida : culms 6-16-noded, 6-12 mm in diameter, very stout, up to 3 m tall; basal leaf-sheaths often flabellate; leaf-blades 10-17 mm wide, glabrous; panicle 20-50 cm long; bristles fulvous.
Cultivars of var. sericea include "Nandi", a diploid, and "Narok", "Kazungula" and "Solander", tetraploids. "Narok" was selected for its cool-season productivity and winter-greenness in frost-prone subtropical environments, but seed production is poor, owing to the low percentage of tillers bearing inflorescences, especially in older seed production stands. This was partially remedied with the release of "Solander", which is similar to "Narok" in winter-greenness and yield but has much higher seed production, associated with higher tiller fertility. "Kazungula" produces more seed than other cultivars, but becomes extremely stemmy when mature. Hybridization between var. splendida and var. sericea and selection in Australia led to the release of the seed-producing cultivar "Splenda", which has yielded well in trials throughout South-East Asia and the South Pacific.
In natural grasslands at moderate to high altitudes in East Africa, setaria can constitute a considerable proportion of the herbage but is rarely dominant. Setaria grows at higher altitudes in the tropics than other panicoid pasture grass species, and this has been associated with evolutionary physiological adaptation to sub-zero night temperatures. Varieties and cultivars differ in their adaptation and yield, although all require a relatively moist environment and have low drought tolerance. In general, setaria cultivars have some tolerance of intermittent waterlogging. "Kazungula" is considered to be one of the better adapted forages for the lowland wet tropics receiving at least 1200 mm annual rainfall. In Malaysia it has been commonly recommended as an improved forage for sowing in smallholdings and commercial enterprises since the early 1970s. "Kazungula" can tolerate brief periods of moisture stress and is suited to well-drained soils of lower fertility. The variety splendida is also well adapted to the humid lowland tropics. "Nandi", "Narok" and "Solander" are better adapted to the subtropics or elevated tropics receiving more than 1000 mm of annual rainfall.
Propagation and planting
Most cultivars and varieties are sown by seed, except for var. splendida , which needs to be vegetatively planted. This has to some extent limited the usefulness of var. splendida in Malaysia and Indonesia. For vegetative planting, plants should be topped to a height of about 15 cm, split into pieces of 2-3 tillers, and planted without allowing them to dry out. Successful establishment usually exceeds 90%, providing the soil remains moist following planting. Setaria seed should be sown at a rate of at least 2 kg/ha. Establishment is most successful in a fully-cultivated seed-bed. Setaria may be sown with a companion legume, such as Centrosema pubescens Benth. or Neonotonia wightii (Wight & Arnott) Lackey, and may produce a stable pasture mixture, although var. splendida and "Kazungula" compete aggressively with legumes and are less suitable for mixed pastures.
Setaria should be grown on a relatively fertile soil or fertilized, particularly with N, if it is to yield to its potential. It responds well to applied N and yields exceeding 30 kg dry matter per kg of N applied have been reported. It also has a high requirement for K. It is tolerant of continuous grazing and high grazing pressures, although the latter would have an adverse effect on most associate legumes. In subtropical Australia, well-fertilized setaria pastures sustained continuous stocking rates of up to 6 steers per hectare. Similar stocking rates could be anticipated in tropical regions without a pronounced dry/cool season.
Diseases and pests
The leaf disease caused by Pyricularia grisea is noted in Australia but is not a serious problem. Inflorescence diseases caused by Sphacelotheca sp. and Fusarium nivale can be serious in Zaire and setaria bunt, caused by Tilletia echinosperma , can devastate seed crops in Kenya. It is considered that there is little likelihood of transmitting this disease in seed, as it is spread from inflorescence to inflorescence in the field. Seed crops in Australia may also be adversely affected by caterpillars.
Setaria is both grazed and fed as cut-and-carry forage and can also be made into hay or silage. Thicker stemmed cultivars, such as "Kazungula" or "Splenda" are less satisfactory for hay than finer stemmed cultivars such as "Nandi".
Annual DM yields of as high as 31 t/ha have been recorded for var. splendida in Indonesia and 19 t/ha under regular defoliation in Malaysia. Trials in Malaysia gave higher DM yields for "Kazungula" than "Narok" or "Nandi", and "Nandi" also yielded poorly in trials at Khon Kaen, Thailand. In Australia, dairy cows grazing var. splendida have produced more milk than cows grazing cultivars of other setaria varieties. In beef-production studies var. splendida and "Narok" produced high levels of animal weight gain, although differences between cultivars are most pronounced during the subtropical cool season.
Setaria is an extremely diverse species which in Africa naturally covers a wide latitudinal and altitudinal range. The existence of various intra-specific taxa, at least some of which can be inter-hybridized, is an indication of its morphological diversity. Germplasm resources are held by ATFGRC (CSIRO, Australia) and a smaller collection by CIAT (Columbia).
Hybridization between ecotypes may be carried out without difficulty. Being a cross-pollinated species, combining inflorescences in a bag when at anthesis results in a high proportion of hybrid seed. However, the existence of an extensive polyploid series is a barrier to gene transfer. Although hybrids can be produced between tetraploids and hexaploids, and between hexaploids and octaploids, they are likely to be unstable as they have an odd number of genomes.
Setaria has been shown to be a successful species in Malaysia and Indonesia, and it can be expected that its usefulness will extend to pasture developments elsewhere in the region. The relatively reliable establishment of setaria when sown by seed is a point in its favour. The new cultivar "Splenda" is likely to take over from "Kazungula", especially in flood-prone and high rainfall environments.
- Blair, G.J., Ivory, D.A. & Evans, T.R. (Editors), 1986. Forages in Southeast Asian and South Pacific Agriculture. ACIAR Proceedings Series No 12. ACIAR, Canberra. 202 pp.
- Bogdan, A.V., 1977. Tropical pasture and fodder plants. Longman, London. pp. 249-261.
- Evans, T. R. & Hacker, J.B. 1992. An evaluation of the production potential of six tropical grasses under grazing. 2. Assessment of quality using variable stocking rates. Australian Journal of Experimental Agriculture 32: 29-37.
- Hacker, J.B. & Evans, T.R., 1992. An evaluation of the production potential of six tropical grasses under grazing. 1. Yield and yield components, growth rates and phenology. Australian Journal of Experimental Agriculture 32: 19-27.
- Halim, R.A. (Editor), 1989. Grasslands and forage production in South-East Asia. Proceedings of first meeting of the regional working group on grazing and feed resources in South-East Asia, 27 Feb - 3 Mar, 1989. FAO, Rome. 216 pp.
- Oram, R.N., 1990. Register of Australian herbage plant cultivars. CSIRO, Australia. pp. 50-53.
- Skerman, P.J. & Riveros, F., 1990. Tropical grasses. FAO, Rome. pp. 662-669.