Variabilidade genética de germoplasma de arroz (Oryza sativa L.) para tolerância ao frio na germinação

Abstract

At the Rio Grande do Sul State low temperatures are one of the main limiting of rice crop, being the cold tolerance a characteristic of difficult selection on field conditions. The utilization of SSR molecular markers combined with phenotypic characteristics provides complete and precise information, enabling the breeder to select more efficiently useful genotypes to the breeding programmes. Therefore, the aim of this work was to study the genetic variability of the genotypes belonging of the rice germoplasm active bank of Embrapa, using morphological characters and SSR molecular markers, to identify the genetic variability in cold tolerance at the germination. The response of the genotypes to cold stress during the germination was evaluated in two experiments; I: 124 rice genotypes and four tolerant controls were evaluated on conditions of temperature of 13 ºC during 28 days and 25 ºC during seven days; there were compared their relative performance, measured by the length of the coleoptile, root and shoot, and germination. II: under oscillation of temperature of 25 ºC during 72 hours, 13 ºC during 96 hours (cold) and again 25 ºC during 72 hours (control) to differentiate the genotypes in terms of cold tolerance by the regrowth of the coleoptiles. There were evaluated 151 genotypes and nine SSR loci. The results obtained indicated that among the studied genotypes of the germoplasm bank of Embrapa, there are broad genetic variability, as well as different stress responses. Then, some genotypes have the potencial to be used in the expansion of the genetic basis in the pre-breeding and breeding programmes of this crop. Based on the phenotypic characterization, the most promising genotypes to cross and obtain superior progenies in terms of cold tolerance were BRS 7-Taim, Rio Grande and EEA 405. In the genotypic characterization, the genotypes in study showed high genetic variability.