Abstract
Large vascular bundles in peduncle and lower elongated internode, and their relations to primary rachis branches of the spike were investigated in a total of 10 rice cultivars belonging to Indica, Hsien (Indica with Chinese origin), Javanica, and lowland and upland types of Japonica. Numbers of vasculer bundles in peduncle markedly varied among the above ecotypes; cvs of Indica and Hsien showed higher numbers from 17 to 25, and consequently the ratios of vasculer bundles to rachis branches (Vb/Rb ratio) were higher than 1.6. On the other hand, cvs of Japonica bore fewer vascular bundles from 10 to 13 and the Vb/Rb ratios showed the range from 0.9 to 1.2. These distinct variations in Vb/Rb ratio were mainly due to the difference in numbers of vascular bundles in peduncle but not in those of lower internode or of basal parts of flag-leaf sheaths. It was discussed with the relation of the differences in Vb/Rb ratios among ecotypes and translocation effeciency of photosynthetic product or the rate of senescence.
