Abstract
The relationship between the vascular bundle system in a peduncle and the yield components was investigated using 29 temperate-japonica rice varieties, Oryza sativa L., which consisted of 22 Japanese and 7 Chinese improved and native varieties. Nine plants of each variety were cultivated in the field in 1998 with two replications. The number of large vascular bundles (Vb) in a peduncle differed significantly between the varieties ranging from 9.6 to 18.9. According to the ratio of the number of Vb to the number of primary rachis branches, V/R ratio, the 29 varieties were divided into 2 groups; those with high (>1.2) and low (<1.2) V/R ratio. No difference was found in heading date between the varieties with high and low V/R ratio, but the culm length and panicle number were respectively, higher and lower in the varieties with a high V/R ratio than in those with a low V/R ratio. The varieties with a high V/R ratio showed a larger number of spikelets and grains on the secondary rachis branches, but no difference was observed in the grain weight between the 2 groups. It was assumed that the excess of vascular bundles in the varieties with a high V/R ratio indicated that the secondary-branch spikelets had developed and well filled with photosynthetic products. The varieties with a high V/R ratio showed a heavier panicle weight, but lower grain weight per plant because of the lower number of panicles as compared with the varieties with a low V/R ratio. The significance of the vascular bundle system in breeding for a high yielding ability was discussed.
