A new generation of improved, hybrid-derived lines of Stylosanthes guianensis has been developed. S.guianensis has a wide application in coastal and subcoastal regions of North Queensland, in areas with higher than 1500mm AAR. These composite hybrids possess quantitative resistance to anthracnose in the native habitat and center of diversity of the species, as well as in vastly different ecosystems.
Composite hybrid-derivatives produced significantly more seed than the control cultivar Mineirão.
Currently just 6kg of basic seed of one anthracnose-resistant cultivar of var. vulgaris is available in Australia. As yet seed of the hybrid is not commercially produced in Australia.
FOR FURTHER INFORMATION
Dr Bela Grof
International Consultant
Forage species evaluation, selection
Tropical pasture research and development
Training
Stylo has a long history of use as a pasture legume species in tropical Australia. The first accessions of "common" stylo (CPI 5630 and 5631) were introduced from Brazil in 1933. Schofield reported in 1941: " stylo shows great promise as a pasture legume of high value, suitable to the tropical conditions of North Queensland, and deserves widespread trial."
Commercial cultivars of S. guianensis selected in Australia were devastated by anthracnose in the early 70s. Stylo anthracnose was first recorded in Brazil in 1937, and now it is known to be widespread where the species is endemic as well as in situations where stylo is an introduced exotic species. Its severity varies among species, botanical varieties and across ecosystems. A high level of susceptibility (over 90%) was recorded among accessions of var. vulgaris, while 60% of the accessions of var.pauciflora evaluated showed resistance to the disease.
For the savanna grasslands of the world, there is a need for new cultivars of the perennial S.guianensis with durable resistance to anthracnose and other biotic and abiotic constraints, early flowering, acceptable seed yields, and retention of green leaves during the dry season.
In spite of the severity of anthracnose affecting S.guianensis in the center of origin/diversity, resistant genotypes of both botanical varieties, var. vulgaris and pauciflora, have been identified in Brazil and Colombia. However, these cultivars (Bandeirante and Mineirão) have well recognised deficiencies, a major one being low seed production.
Heterogeneous populations derived from intervarietal crosses of S.guianensis were developed by Dr John W. Miles at CIAT, Colombia and have been under evaluation at CNPGC Brazil since 1991.
Bulk populations have been formed by physically mixing seed from anthracnose resistant single plant selections of similar phenology, seed yield, and morphological characters.
For the final evaluation of stability of disease resistance, general agronomic performance and adaptation to a wider range of ecological conditions composites of selected hybrid lines were used and were tested in regional trials in Brazil.
Selections representing early and mid-season maturity types were contrasted with a late maturity type, a composite of four and another composite of two hybrid-derived lines were included with a resistant and one susceptible control in small plot trials under a cutting regime. The regional trials were located along a north-south transect of the Cerrados from lat. 6°09'S to lat.20°27'S.
A new generation of improved, hybrid-derived lines of S.guianensis has been developed. These composite hybrids possess quantitative resistance to anthracnose in the native habitat and center of diversity of the species, as well as in vastly different ecosystems. Composite hybrid-derivatives produced significantly more seed than the control cultivar Mineirão. Currently no commercial anthracnose-resistant cultivar of var. vulgaris is available in Australia. S.guianensis has a wide application in coastal and subcoastal regions of North Queensland, in areas with higher than 1500mm AAR.
Do not hesitate to contact Dr Bela Grof for further information.
International: +61-7-544-59233
International: +61-7-547-88267
The impact area-savanna grasslands
Tropical savannas constitute the largest areas of undeveloped land resources in the world.
The pasture problem
Although these grasslands support large populations of livestock, productivity is generally low. Poor nutritive value of native pastures and sown monospecific grass swards is the principal cause of this low productivity, especially in the dry season when native grasslands often provide no more than 60% of the animal's maintenance requirements. A fundamental approach in correcting nutrient deficiencies is through the establishment of improved pastures based on tropical legume-grass mixtures.
The potential of tropical savannas is very large for pasture-based livestock systems. Efficient use of resources is essential for economically viable and sustainable production systems. Most savanna ecosystems have serious problems of resource degradation, soil erosion, over grazing and marginal economic viability.
The goal
To identify forage legumes resistant to biotic and abiotic stresses which are also adapted to grazing utilisation, produce high yields of good quality forage and commercially acceptable seed yields.
Legume germplasm
New strategies and, in some cases, new germplasm and technology are needed to counter the problems associated with legume-based pasture development. Specific objectives, like disease resistance, always require new germplasm and we are in that position now for Stylosanthes guianensis.
Tropical grassland agriculture in Australia and other countries benefited from forage plant exploration and domestication of wild leguminous species introduced from the New World tropics. The genus Stylosanthes is a case in point.
Research activities
The search for adapted forage species was conducted by the Tropical Pasture programme of the International Center for Tropical Agriculture (CIAT) in the lowlands of tropical America over 25 years.
The writer initiated forage germplasm introduction, exploration and follow-up evaluation/selection projects with centers of operation in the Llanos of Colombia and at two sites in the Brazilian Cerrados. These savanna ecosystems are the center of origin/diversity of several Stylosanthes spp.
During the early stages of the evaluation programme Stylosanthes guianensis seemed to be the logical choice. However, as it was soon discovered, the native habitat and center of diversity of the species is also the center of diversity of its specialised pathogens. In the initial experiments of CIAT, in Brazil as well as in Colombia, the S.guianensis var. vulgaris or "common" stylo accessions were devastated by anthracnose (Colletotrichum gloeosporioides Penz. et Sacc).
To control stylo anthracnose and develop new cultivars of forage species the programme initiated a
two-pronged attack.
First, the emphasis was shifted to other species of Stylosanthes. Evaluation and selection of cultivars from other genera and species was the other avenue of research.
Specific results
In Colombia, anthracnose-resistance and adaptation to acid, infertile sandy soils was discovered in accessions of Stylosanthes capitata, a species formerly unknown to agriculture (Grof et al.1979.Trop.Grasslds, 28-37 ).
Contributions to tropical pasture technology included the identification of a number of successful tropical pasture plants, amongst them, Andropogon gayanus, Brachiaria spp., Paspalum atratum, Arachis pintoi, Centrosema spp., Desmodium ovalifolium.
Genetic diversity to control anthracnose
A strategy of anthracnose control was devised in a Stylosanthes improvement project conducted at the National Beef Cattle Research Center (CNPGC) of the Brazilian Research Corporation (EMBRAPA) at Campo Grande in the State of Mato Grosso do Sul, Brazil. Disease restriction by genotype mixtures was highly effective in case of an interspecific mixture of S.capitata and S.macrocephala in Brazil where a high percentage (85%) of the accessions of S.capitata evaluated was susceptible to virulent races of anthracnose.
Hybridisation among accessions of S.capitata of Brazilian and Venezuelan origin produced recombination of the desirable traits of each parental ecotype, i.e.: the high forage dry matter yields of the Brazilian accessions and anthracnose-resistance of the Venezuelan ecotypes. Genetic diversity was further increased by physically mixing seeds of accessions of S.macrocephala and the bulked composite of S.capitata.
This multicross cultivar is highly resistant to anthracnose in the native habitat and center of diversity of the species (Grof et al. XVIII. Int.Grassld.Cong. Session 4-31.)
Development of a composite hybrid cultivar of Stylosanthes guianensis
Stylosanthes guianensis subsp. guianensis var. vulgaris, or "common" stylo, is widely distributed from Mexico through to Argentina. The species is native to savanna habitats and it is well adapted to low fertility situations. It shows very wide morphological variation. In Brazil, two important botanical varieties have been described, var.vulgaris and S.guianensis subsp. guianensis var. pauciflora.
Selection was carried out for disease resistance and desirable agronomic traits over five generations, three grown in Campo Grande and two in two different sites in the Philippines, under conditions of 2000mm or 4000mm annual rainfall. Although these populations were reported to be resistant to anthracnose in Colombia, several of them succumbed to the disease in the Brazilian Cerrados ecosytem. Field observations on response to anthracnose were supported by spray inoculation of populations with virulent pathogenic races of Brazilian origin in the glass house.