Estimação de parâmetros genéticos e índice de seleção em genótipos de Brachiaria brizantha

Abstract

Nowadays, the Brachiaria brizantha is the tropical grass with greatest cultivated area in Brazil, being responsible by a major part of the seeds market and by the increase in animal production. Many are the superior genotypes in relation to commercial genotypes available in the germoplasm banks, that were collected in the African Continent and need evaluations. The selection of these genotypes must be based on predicted genotype values of the individuals in function of being perennial plants and of unsexed propagation The standard procedure for the prediction of genetic values is the individual BLUP (Best Linear Unbiased Predictor), using estimates of variance components achieved by the restricted maximum likelihood (REML) under individual model. With the aim of selecting B. brizantha materials superior to the commercial cultivars in relation to the agronomic traits, 213 genotypes were evaluated in four experimental fields in the Embrapa Gado de Corte in Campo Grande, MS. The fields were conducted in different times, being that field one was evaluated through three years, and the others through two years. The agronomic traits evaluated were: vigor, growth, total dry matter (MST), green dry matter (MSV) leaves percentage (PF), leaf dry mater (MSF). The utilized experimental design was that of randomized blocks in three replications, being the cultivars Marandu and Xaraés the witnesses. The best repeatability and heritability coefficients were found to leaves percentage (0.51 and 0.51) and growth (0.44 and 0.41), respectively, indicating that these estimates are good selection parameters. The genotypes with greater predicted genetic value by the additive selection index were: B72, B188, and B252, with a performance 24, 20, and 21% superior to the Marandu cv., respectively, to the fields one, two, and four. Yet the results attained in in field three in relation to the index indicated superiority (26%) of the Xaraés cv. In relation to the Marandu cv.. Through the results of the evaluation of the predicted genetic effects it was possible to organize a ranking of the most promising genotypes, being that B72 and B178 were the best for leaf dry matter in the wet and dry seasons , and B252 and B172 for leaves percentage, and B252 and B71 for growth.