Abstract
In this study the correlation of grain weight with the date of anthesis and the nodal position of glumaceous flower was analyzed. The weight growth of grains on both the primary (PR) and secondary rachis-branches (SR) proceeded from the higher to the lower nodal position in the panicle after heading. The final grain weight in each nodal position was heavier on PR than on SR. On SR, the final grain weight was clearly heavier in the higher position than in the lower position in all cultivars. However, there was no difference in grain weight among each nodal position on PR. On both PR and SR, flowering initiated from higher to lower position irrespective of cultivar. On SR the grain weight correlated positively with the flowering order; early flowering spikelets tended to have heavier grains than late flowering spikelets. On PR, however, no significant correlation was observed between the grain weight and flowering order. Dry weight of both leaf blade and leaf sheath decreased consistently over the ripening period. On the other hand, culm dry weight slightly decreased after the heading time but reincreased at the middle or late stage of the ripening. These results suggested that the nodal variation in grain weight on the SR was not caused by the shortage of photosynthate in the leaf and stem (leaf sheath and culm), but by the branching structure of panicle, the decrease in sink capacity and other factors.
