Digitaria eriantha (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Digitaria eriantha Steudel

Protologue: Flora 12: 468 (1829).

Family: Gramineae

Chromosome number: 2n= 18, 27, 36, 45, 50, 54

Synonyms

Digitaria smutsii Stent (1924), D. decumbens Stent (1930), D. pentzii Stent (1930), D. valida Stent (1930) , D. pentzii Stent var. stolonifera (Stapf) Henrard (1950); D. eriantha Steudel with 4 subspecies: ssp. eriantha, ssp. pentzii (Stent) P.D.F. Kok (1981), ssp. stolonifera (Stapf) P.D.F. Kok (1981), ssp. transvaalensis P.D.F. Kok (1981).

Vernacular names

• Common finger grass, digit grass (also used for other spp.), pangola or pongola grass ( Digitaria decumbens ) (En).

Origin and geographic distribution

D. eriantha is a species of subtropical southern Africa. A single clone, commonly referred to as pangola grass, is now widespread in grazing areas throughout the world's humid tropics and subtropics, including South-East Asia, having been extensively planted from the 1960s to the 1980s. Many other lines have been distributed for evaluation.

Uses

It is utilized extensively as a grass for grazing, mostly with N fertilization rather than a companion legume. It is also utilized as a hay crop.

Properties

D. eriantha is often considered to be one of the higher quality tropical grasses. Pangola grass has been extensively studied but there is relatively little information on other genotypes. Pangola grass has an N concentration of (0.5-)1.5-2.0(-4)%. Phosphorus concentration can be too low for livestock on low-P soils in the absence of P fertilizer. Dry matter digestibility varies between 45-70%. Pangola grass has relatively high concentrations of Na in its tissues, compared with many other tropical grasses.

Description

More or less robust perennial, growing either as a dense tussock, with or without extended stolons or as a continuous stoloniferous sward. Stolon internodes with or without hairs. Culms erect or ascending, sometimes rooting at the nodes, to 1.5 m tall. Leaf-sheath scabridulous, glabrous to hairy; ligule subtriangular, 2-4 mm long, shortly ciliate; leaf-blade linear, 5-60 cm × 1.5-12 mm, glabrous or hairy, but minutely scaberulous on both surfaces. Inflorescence a racemose panicle, composed of 3-14 erect racemes 6-18 cm long, borne in loose whorls and with some racemes single on an axis up to 7 cm long; spikelets 2-4 mm long, conspicuously hairy; lower glume to 0.5 mm long, the upper _ as long as the spikelet and appressed hairy; lower lemma minutely hairy, characteristically with 7 smooth rather than scabrous nerves. Many clones are sterile or almost sterile.

Growth and development

In subtropical areas, pangola grass flowers in mid-summer; flowering time differs with other genotypes, with cultivar "Premier" (ssp. eriantha in the sense of Kok) flowering in late spring and again in autumn.

Other botanical information

D. eriantha is extremely diverse but it is probable that 80% of agronomic publications are concerned with a single genotype. Performance data should therefore not be generalized for the species as a whole. D. eriantha is closely related to the tropical D. milanjiana (Rendle) Stapf, from which it may only be distinguished by the absence of scabrosity on nerves of the lower lemma, a characteristic which may be difficult to determine, even with a lens. Frequently in the agronomic literature, accessions are described simply as Digitaria sp., which is of little help when documenting species characteristics.

In the taxonomic literature, the tremendous variability of this species has resulted in numerous names and subclassifications (see Synonyms). Much more research is needed to unravel the D. eriantha complex. In 1981 Kok distinguished 4 subspecies for the South African taxa, but in 1984 he reduced them to synonyms of the whole species complex. Two seed-producing cultivars, "Premier" and "Advance", belonging to D. eriantha ssp. eriantha (in the sense of Kok), have recently been released in Australia. Pangola grass belongs to D. eriantha ssp. pentzii (in the sense of Kok), and cultivars "Taiwan", "Transvala" and "Slenderstem" have been developed in the United States from southern African introductions of this subspecies.

Ecology

Accessions of ssp. pentzii (in the sense of Kok) (pangola, "Slenderstem") are recommended in Malaysia and the Philippines for poorly drained soils. They are tolerant of flooding, and any areas where the grass dies out are rapidly re-invaded by stolons from the surrounding sward. Pangola grass is intolerant of shade and is therefore not suitable for integrating with plantation agriculture, but can grow on a wide range of soil types from sands to heavy clays. Cultivars "Premier" and "Advance" are adapted to sub-humid subtropical conditions and they have markedly better cool-season growth than other cultivars. In general, the seed-producing lines of the species tend to be better adapted to sandy loam soils as seedling establishment can be difficult on heavier soils. However, once satisfactorily established, they also grow vigorously on clays.

Propagation and planting

Stoloniferous genotypes are planted vegetatively. Actively growing swards are allowed to become stemmy and are then cut and the material spread on a cultivated surface at 0.5-2 t of green matter per hectare. This is then disked in, or trampled in by cattle if the ground is too wet for implements. In warm moist environments, pastures establish rapidly by this method and in general weeds are suppressed by the planted grass. Seed-producing cultivars such as "Premier" and "Advance" require a reasonable seed-bed for establishment and an absence of serious competition in the early stages. Establishment is most satisfactory on sandy to sandy-loamy soils. Once established, however, they have the capacity to thicken up and spread from the sown area. D. eriantha is an aggressive species and does not generally combine well with pasture legumes.

Husbandry

Once established, D. eriantha tolerates heavy stocking rates. On infertile soils it benefits from heavy fertilizer application, especially N. Stoloniferous cultivars can become sodbound and may benefit from periodic renovation by disking.

Diseases and pests

Susceptibility to the rust Puccinia oahuensis a widespread disease occurring in the Americas and Australia, varies between genotypes, with "Transvala" showing some resistance. The most serious disease of D. eriantha is pangola stunt virus, a dwarfing disease which has seriously reduced the usefulness of pangola since it was first reported in Surinam in 1960. The disease is transmitted by an aphid, Sogatella furcifera, or in Australia by the related S. kolophon. "Transvala" has some resistance to this disease but trials in Australia on a number of lines of digit grasses failed to show any resistance.

Insects which cause damage include spittlebugs ( Tomaspis flavopicta, T. humeralis , Prosapia bicincta ) in Brazil and Taiwan, Rhodes grass mealy bug ( Antonina graminis ) (also in Brazil and Taiwan), chinch bug ( Blissus leucopterus ) in Taiwan, sugar-cane aphid ( Sipha flava ) in the Caribbean region and Taiwan, army worms ( Laphigma spp., Spodoptera spp. and Mocis spp.), and the root-knot nematodes Belonolaimus longicaudatus and Platylenchus brachyurus in the Americas.

Harvesting

D. eriantha is usually grazed, but is also suited to cut-and-carry feeding systems or hay making.

Yield

Herbage DM yields as high as 36 t/ha per year have been reported for pangola grass, but production is more normally in the range 11-22 t/ha per year. Beef production from N fertilized pangola can exceed 1000 kg/ha per year. Grown with tropical legumes, "Transvala" digit grass produced an average liveweight gain of 350 kg/ha under continuous grazing at a stocking rate of 2.6 steers/ha in Malaysia. From ssp. eriantha (in the sense of Kok) in South Africa, beef production ranged from 84-110 kg/head per season at a stocking rate of 7.5 animals per hectare. Milk yields of 6000 kg/ha per year have been obtained from well-fertilized pangola grass pastures.

Genetic resources

Germplasm collections are available at ATFGRC (CSIRO, Australia).

Breeding

There is a continuing interest in selecting and breeding D. eriantha and the closely related D. milanjiana , with which it is often confused.

Prospects

Future work is likely to result in the commercialization of seed-producing cultivars which should extend the usefulness of this important species.

Literature

• 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. 111-122, 124-126.
• 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.
• Kok, P.D.F., 1984. Studies on Digitaria (Poaceae) 1. Enumeration of species and synonymy. South African Journal of Botany 3: 184-185.
• Oram, R.N., 1990. Register of Australian herbage plant cultivars. CSIRO, Australia. pp. 105-106.

Authors

J.B. Hacker