Factors affecting the ripening process of different rice cultivars.

In order to make clear the factors affecting the ripening, four cultivars (Nanching 11, Suweon 258, Akenohoshi and Yamabiko) were examined on ordinary paddy field. The former three cultivars produced about 40, 000 grains/m2 and cv. Yamabiko did 27, 000/m2 at 3.5-5 of maximum leaf area index each. Yields of brown rice were ranging 5-6 tons/ha on all cultivars. The percentage of fully ripened grains in each cultivar, which expressed by the ratio of weight of 1, 000-whole-grains to weight of 1, 000-winnowed grains, was obtained as follows, 93% in cv. Yamabiko, 80% in cv. Nanching 11, 77% in cv. Suweon 258 and 73% in cv. Akenohoshi. The weight of 1, 000-raw-grains at 15 days after heading showed a high positive correlation to 1, 000-whole-grains of harvest time in all cultivars (r=0.978). It seemed that the final weight of 1, 000-whole-grains was strongly affected by a volume of young kernel at the milk-ripe stage. The weight of raw-grain, showing kernel's volume, highly correlated to the sucrose content per grain at 5 days after heading in each cultivars (r=0.981). As a result of multiple regression analysis, both factors the leaf area per grain and the rachis-weight per grain, could be expronated the sucrose content per grain at 5 days after heading, i.e., standard partial regression coefficients were shown 0.786 in the former and 0.431 in the latter (R=0.936), respectively. It is concluded that the highest value of ripening of cv. Yamabiko owed to its highest amount of the leaf area per grain among the four cultivars.