TEODARDO CALLES1, RAINER SCHULTZE-KRAFT1, ORLANDO GUENNI2
1University of Hohenheim, Institute of Plant Production and Agroecology in the Tropics and Subtropics, Department of Biodiversity and Land Rehabilitation, Germany
2Central University of Venezuela (UCV), Maracay, Department of Agricultural Botany, Section: Agricultural Ecology, Venezuela
The primary importance of Stylosanthes - probably the most widely used tropical forage legume genus - lies in the particular potential of most species for marginal conditions, due to their adaptation to low-fertility soils and drought. There are about 40 species, among them the well-researched S. humilis, S. guianensis, S. hamata, S. scabra, S. capitata, and S. macrocephala.
The current importance of Stylosanthes is reflected by numbers of cultivars and of hectares sown, and volumes of seed produced. So far, there are more than 30 formally released and informal cultivars, mainly within the aforementioned species. Many of them, however, have never been used to any significant extent. Stylosanthes is particularly important in Australia, tropical China, India, Thailand and West Africa. It is used for grazing in mixtures with grasses or in fodder banks, for improvement of communal grazing lands, and increasingly also for leaf meal production. The main production-limiting factor is anthracnose. Lack of both continuity in research and effective extension mechanisms has also constrained further variety development and adoption.
The potential importance is defined by the inter- and intra-specific variability. Stylosanthes species have a wide natural distribution, are highly polymorphic and show mechanisms of adaptation to the most variable environments and ecological niches. Available Stylosanthes germplasm constitutes the world's largest collection of a tropical forage legume, the vast majority of accessions belonging to the aforementioned species. Of those, the potential of S. humilis and S. capitata has not yet been explored adequately; they deserve a research revival. A number of Stylosanthes species are still essentially unknown to agronomists and are poorly or not at all represented in germplasm collections. However, because of particular, promising characteristics, they are considered worth of germplasm collection and evaluation efforts, such as S. fruticosa, S. leiocarpa, S. mexicana, S. sericeiceps and S. sympodialis. Other, though not particularly productive, species deserve attention as potential source of genes for breeding programs such as S. angustifolia, S. bracteata, and S. tuberculata. As a successful example from Brazil shows, unconventional variety development approaches should be considered as should participatory research with farmers and uses other than for grazing.
Keywords: Cultivars, current importance, forage legumes, genetic resources, potential importance, Stylosanthes