HETEROSIS AND COMBINING ABILITY FOR GRAIN YIELD AND EARLINESS IN ACCESSIONS OFA RICE CORE COLLECTION

Rice has extensive collections of germplasm, but a small fraction of genotypes are used in breeding programs worldwide. This aimed to assess the heterosis and the combining ability for higher grain yield and earliness, and their correlations to genetic distance among accessions belonging to the Embrapa´s Rice Core Collection. Crosses were made in complete diallel, without the reciprocals, being phenotyped in generations F2 and F7for grain yield (GY) and days to flowering (DTF). It were estimated the varietal effect, mean heterosis, varietal heterosis, specific combining abilityand general combining ability (GCA) of the parents in each generation. For the selection of new lines, the combinations involving the genitors with the highest magnitudes and positive effects for GCA were onsidered more promising for the GY, of which Canela Curta, Maninjau, Epagri 108 and Diamante stood out, and were also the most productive. For the DTF, the genitors with the largest earliness estimates were Araguaia, CT11632, Irat 122, Pratinha Branco and Tox 503. The recommended parameters for estimating GY in F7 eneration from the data of the F2 generation were the mean of GY, GCA and the mean Rogers-W genetic distance coefficient. Crosses with Rogers-W distance coefficients above 0.9 showed higher GY and earliness in F7 generation, whereas in F2 the superior crosses were those that showed Rogers-W between 0.7 and 0.89. The above genotypes and the specific combinations identified may lead to new rice cultivars.