Abstract
We examined the nodal distribution of the numbers of ripened and empty grains and the grain weight in the panicle in 12 rice cultivars with different cold tolerancecultivated in cool water(daily mean temperature, 19C). The number of grains including empty ones did not vary so much with the nodal position on the primary rachis-branches, but was high at the middle part on the secondary rachis-branches. This tendency was stronger in cold tolerant cultivars, and the number of ripened grain at each nodal position on the panicle was also higher in cold-tolerant cultivar. The nodal variation in grain weight was larger on the secondary than on the primary rachis-branches in all cultivars. On the secondary rachis-branches of the cold-tolerant cultivars, the lower the nodal position, the higher the fertility percentage, but the weight of each grain negatively correlated with the fertility percentage, In the cold-tolerant cultivars fertility percentage was higher in the order of lower>middle>upper pa of panicles, and in the order of tertiary>secondary>primary rachis-branches. This tendency was not clear in the cold-susceptible cultivars. Participation of assimilate transport from stems and leaves in the negative correlation between the fertility percentage and gain weight remains to be examined further.
