Tropical Forage Breeding in Embrapa: Current Situation and Prospects

摘要

Animal production in the tropics is generally carried out on native and cultivated pastures. The present scenario has shifted from extensive production to sustainable utilization of natural resources, optimizing inputs and income as a result of ecological, economical and market demands. Thus, cultivated pastures, previously restricted to marginal areas in the farms, now compete with crops for fertilizers and technology. Better, more productive pastures require improved cultivars, thus justifying investment in breeding and selection programs. The area covered by cultivated pastures in Brazil doubled in the last 20 years (-100 million hectares), due largely to the use of Brachiaria and Panicum. However, few cultivars are available, which result in dangerously low diversity, since both reproduce primarily through apomixis, or asexual seed production. Both these African grass genera are being bred at Embrapa Beef Cattle Center with the objective of releasing new cultivars. Brachiaria has shown remarkable plasticity in adapting to poor and acid soils of the Brazilian savannas, in a variety of climates and altitudes, competing well with weeds and displaying good animal performance. Panicum maximum is a high producing, high quality forage, mostly for rainy season utilization in soils of better fertility. These breeding programs have identified superior genotypes, which resulted in the release of cvs. Tanzania-1, Mombaca and Massai of P. maximum and cv. Marandu and Xaraes of Brachiaria. Intra and interspecific hybrids have been produced and are at different stages of evaluation in the process of cultivar development. Important traits considered are production, resistance to insects/diseases, nutritive value, adaptation to different ecosystems, and goodseed production. The forage breeding program at Embrapa Beef Cattle Center encompasses also a native legume, Stylosanthes, which has good nutritive value and palatability, and establishes well in mixtures with Brachiaria allowing for sustainability of the pasture through its good nitrogen fixing ability. The Stylosanthes program has identified anthracnose resistant/productive genotypes and research is directed at identifying genetic diversity among populations of three species of major agronomic importance, while using molecular markers to identify outcrossing rates. Embrapa released two cultivars: cv. Mineirao of S. guianensis and cv. Campo Grande - a seed mixture of lines of S. capitata and S. macrocephala bred and selected independently. For the development of cultivars there are important pre-requisites: germplasm collections, information on genetic diversity available for the problem(s) at hand, study of mode of reproduction/breeding behavior, ploidy level, and inheritance of traits of importance. Despite years of research, information is still much needed for efficient breeding in tropical forages. The cultivar development process is a long term investment: it involves evaluation in plots, regional trials of selected lines for estimation of genotype x environment interaction, and grazing trials for animal performance results. Multidisciplinary teams are essential for successful release and adoption of new cultivars.