Abstract
Grain ripening was examined in the rice cultivar, Hokuriku 130, which has very large grains and is high yielding. In the eight genotypes with a wide range of grain size. width of brown rice grain showed a plateau at 3.6mm. after the hull width exceeded 4.3 mm. Hence in the genotypes with a hull width exceeding 4.4 mm, the grain ripening was unsatisfactory leading to a decrease in grain ripening (lower husking ratio). In the Hokuriku 130, the hull was 4. 1 mm wide and the cultivar exhibited the highest husking ratio. When Hokuriku 130 was compared with a standard cultivar Koganebare, it gave a considerably higher yield because the 1-grain weight was 85-89% larger with a comparable percentage of ripened grains although the number of spikelets per m2 was 34-40% lower. In addition, the percentage of the grains on the primary rachis-branches was remarkably higher which obviously contributed to the higher percentage of ripened grains. It is suggested that the good ripening characteristics of the Hokuriku 130 were due to the higher percentage of grains on the primary rachis-branches resulting from the smaller number of spikelets per panicle and the suitable hull width which offers good grain ripening.
