Genetic variation and association of embryo size to rice seed and seedling vigour

Rapid seed germination and seedling growth would facilitate early plant establishment and better weed competition in direct seeded rice (Oryza sativa L.) culture. Sixty seven indica and 38 japonica cultivars were evaluated for embryo weight and grown in the field, and the harvested seed evaluated for seed and seedling vigour. Seedling growth was evaluated in phytotron. Emrbyo weight and length were largerin japonicas than in indicas. Genetic coefficient of variation is higher for embryo weight and ratio of embryo/endosperm weight (EER) and moderate for embryo length. Very high estimates of heritability in broad sense for embryo weight, length, and EER were indicated. Highly significant correlations of embryo weight with embryo length, kernel breadth and kernel thickness were obtained in the two varietal groups. Embryo weight correlated strongly with endosperm weight and 100-seed weight in indicas, the corresponding correlations in japonicas are low. Path analysis indicated maximum direct contribution to embryo weight by endosperm weight, embryo length and EER in indicas and EER and endosperm weightin japonicas. Correlation coefficients of embryo weight in indicas were positive with seedling height and top dry weight and negative with leaf extension index and seedling tiller number. In japonicas, embryo weight correlated positively with the leaf expansion rate and negatively with seedling leaf and tiller number. Embryo weight and length correlated strongly with shoot length and seedling dry matter in indicas and negatively with root length and percentage germination in japonicas. Embryo length is a reliable index for selection of rice germplasm and breeding materials for desired embryo size.