Seed size, an imperative trait for seed vigor and drought tolerance in rice

Seed vigor is an important trait for direct-seeded rice. Many environmental and genetic factors during seed development stages influenced the seed vigor. As a result of limited source during the reproductive stage, the seeds differ in size within a seed lot due to differential seed filling. This may influence the seedling establishment and drought tolerance ability of the genotype which, however, is less studied. In this regard, the objective of this study was to assess the influence of seed size on seed germination, vigor and drought tolerance in rice. Seeds of six rice genotypes were separated into large and small size. Seed length, width and weight showed significant variation between large and small groups within the genotype. The seedling vigor was higher in larger seeds in all the genotypes. Seed reserves content was also higher in large seeds than in small seeds except for two genotypes. In limited nutrient supply conditions, root length was significantly increased in larger seed seedlings. However, under sufficient nutrient supply, shoot length was significantly increased than root length in larger seed seedlings. Under drought conditions, seedlings from larger seeds showed lower superoxide accumulation and membrane damage indicating higher drought tolerance. Higher seed vigor through better root growth and activation of drought tolerance mechanisms was found to be the key factor for survival during seedling establishment stage.