Influences of the Size of Vascular Bundle at the Neck Internode and Carbohydrate Translocation on Varietal Difference of Ripening Ability of Various Rice Cultivars

Abstract

The influence of the size of vascular bundle and carbohydrate translocation on the ripening ability of rice were investigated with high-yielding varieties bred in Asian countries and Japanese varieties. The percentages of ripened grains in whole panicle (R), on primary rachis-branch (R₁) and on secondary rachis-branch (R₂) were lower in high-yielding varieties. The relations among the amount of carbohydrates increased during the period from heading to maturing per paddy (ΔC/N), that of carbohydrates in stem during the same period per paddy (T/N), and the percentage of ripened grains, were analyzed. T/N in high-yielding varieties showed a significant positive correlation with R, R₁ and R₂, and also with the total area of large vascular bundles per paddy (Vb/N). These significant correlations, however, were not observed in Japanese varieties. Moreover, multiple regression analysis on the percentage of ripened grains indicated that Vb/N strongly contributed to R₂ in high-yielding varieties. These results showed that cultivars with a larger Vb/N have a higher T/N. Such cultivars may have a higher R mainly due to the increased R₂. However, it was suggested that the size of vascular bundle did not directly affect the ripening ability in Japanese varieties because other factors also influenced the translocation of carbohydrate.