Digitaria milanjiana (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Digitaria milanjiana (Rendle) Stapf

Protologue: Fl. Trop. Afr. 9: 430 (1919).

Family: Gramineae

Chromosome number: 2n= 18, 36, 54

Synonyms

Digitaria swynnertonii Rendle (1911), D. endlichii Mez (1921), D. setivalva Stent (1924), D. mombasana C.E. Hubbard (1926), D. polevansii Stent ssp. peterana Henrard (1950).

Vernacular names

• Digit grass, (woolly) finger grass, Milanje finger grass (En, not restricted to this species)
• Thailand: ya mardi digit (for "Mardi").

Origin and geographic distribution

D. milanjiana naturally occurs in tropical East and southern Africa, from Ethiopia and Somalia southwards to South Africa. It has been introduced as a fodder grass to other tropical areas, including several countries in South-East Asia.

Uses

D. milanjiana is used as a forage for grazing by cattle and goats. It has also proved to be useful in banana plantations in tropical Australia for the control of burrowing nematodes.

Properties

Nitrogen concentrations of the cultivar "Mardi" ranging from 1.3-3.0% have been recorded in Malaysia. In Australia, genetic differences in leaf Na concentration of 0.01-2.30% of the dry matter were shown to be associated with provenance, the high Na ecotypes being of coastal African origin. Differences in leaf digestibility were also demonstrated.

Botany

Perennial with erect or geniculately ascending culms to 2.5 m tall from a loosely tufted more or less rhizomatous base, sometimes stoloniferous. Culm nodes glabrous, rarely hairy. Leaf-blade 15-30 cm × 3-13 mm, the blade and sheath more or less hairy to densely villous. Inflorescence a digitate or subdigitate panicle with 2-18 racemes on an axis up to 6 cm long, the racemes 5-25 cm long; spikelets paired on a triquetrous winged rachis, lanceolate, usually 2.5-3 mm long; lower glume 0.2-0.5 mm long, the upper _-_ as long as the spikelet; lower lemma as long as the spikelet, 7-nerved, more or less hairy and with shortly ciliate margins, the nerves characteristically scabrid and often with stiff spreading brown glassy bristles. Caryopsis ellipsoid, greyish-brown.

In subtropical latitudes D. milanjiana flowers freely during the growing season. In the tropics, flowering time appears to be more seasonal and seed set is often poor. It is extremely variable in growth habit and with regard to presence or absence of setae (spiny bristles) on the lemmas. Genotypes which have these setae are frequently referred to as D. setivalva. The essentially tropical D. milanjiana may be distinguished from related subtropical taxa (e.g. D. eriantha Steudel) by the presence of scabrosity along the outer nerves of the lower lemma. Due to the extreme variability, the taxonomy of D. eriantha is complicated. In the literature, both narrow and wide species concepts have resulted in numerous names and subdivisions. More research is needed to solve all problems of this complex.

Cultivar "Mardi" has been released in Malaysia and "Jarra" in tropical Australia.

Ecology

D. milanjiana occurs naturally in a wide range of habitats which are mostly subject to some degree of disturbance, at altitudes up to 2000 m, with an annual rainfall of 400-800 mm. It is well-adapted to the humid lowlands of Malaysia and cultivar "Mardi" (generally referred to as D. setivalva ) is suitable for peat and alluvial soils. The cultivar is recommended for smallholdings and commercial enterprises on well-drained, fertile soils and can tolerate brief periods of moisture stress. It is neither shade-tolerant nor tolerant of waterlogging. It is reported to combine well with Leucaena leucocephala (Lamk) de Wit on alluvial soils in Malaysia.

Ecotypes have been shown to differ in seed-dormancy depending on provenance. Accessions from regions with a protracted dry season have an extended period of dormancy which may be broken by high temperature.

Agronomy

"Mardi" is vegetatively propagated. Stolons are planted into a cultivated seed-bed and, provided the seed-bed is kept moist, intervening spaces are rapidly filled in. Vegetative propagation should be carried out in the first half of the growing season, so as to allow sufficient time for the cuttings to establish.

Some accessions of D. milanjiana produce adequate quantities of seed for commercial seed production. The conditions necessary for good establishment from seed are likely to be similar to those required by other small-seeded tropical grasses.

D. milanjiana is susceptible to pangola stunt virus, but this is not a major problem in Malaysia.

Annual DM yields of 25 t/ha have been recorded in Malaysia for "Mardi" in trials which were harvested every 6 weeks. Swards of D. milanjiana should be grazed relatively frequently to prevent them from becoming too stemmy. A grazing trial in Malaysia on "Mardi" indicated that higher stocking rates could be maintained better on rotationally grazed pastures than on set-stocked pastures. The optimal stocking rate in Malaysia, when fertilized with 150 kg/ha per year of N, is 20-40 goats/ha, giving a liveweight gain of 450 kg/ha per year. Also in Malaysia, liveweight gains of cattle of from 700-1200 kg/ha per year have been recorded from the same cultivar given N fertilizer, although with a high level of year-to-year variation. Milk yields of 16.4 kg/day have been obtained from Friesian cows grazing a genotype selected for high leaf digestibility in Australia, in the absence of any supplementary feeding.

Genetic resources and breeding

Germplasm collections are held by ATFGRC (CSIRO, Australia). Selection trials have identified promising accessions in Australia and Malaysia. Experimental breeding studies in Australia have contributed to an understanding of variation in a number of morphological, developmental and chemical attributes.

Prospects

D. milanjiana is a species with considerable potential. Its extreme variability leads to the possibility of developing improved cultivars for both the wet and seasonally dry tropics. Cultivars with higher seed yields than "Mardi" are needed and there are reasonable prospects for achieving this as seed production is very variable between accessions.

Literature |1 | Clayton, W.D. & Renvoize, S.A., 1982. Gramineae (Part 3). In: Polhill, R.M. (Editor): Flora of tropical East Africa. A.A. Balkema, Rotterdam. pp. 647-649.

• Hacker, J.B., 1988. Polyploid distribution and seed dormancy in relation to provenance rainfall in the Digitaria milanjiana complex. Australian Journal of Botany 36: 693-700.
• Halim, R.A. (Editor), 1989. Grassland 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.
• Lowe, K.F., Moss, R.J., Cowan, R.T., Minson, D.J. & Hacker, J.B., 1991. Selecting for nutritive value in Digitaria milanjiana. 4. Milk production from an elite genotype compared with Digitaria eriantha ssp. pentzii (pangola grass). Australian Journal of Experimental Agriculture 31: 603-608.

Authors

J.B. Hacker & C.C. Wong