Abstract
The varietal difference in the effect of the amount of basal nitrogen application (BNA) on the occurrence of white immature kernels (WIK) was examined using 22 rice varieties and lines (simply called varieties here after) to clarify the effective amount of BNA for the selection of varieties with high husked rice quality under high temperature conditions during the ripening period (RP). In many varieties, white-based kernels (WBK) decreased with the increase in the amount of BNA and improving the state of nutrition during the RP, while milky-white kernels (MWK) increased with increasing number of spikelets per panicle and decreasing allocation of carbohydrates to each spikelet. Moreover, the increase rate of WIK with increasing the amount of BNA varied with the variety, i. e., the number of MWK greatly increased in Fusaotome and Nangokusodachi, that of WBK greatly decreased in Hitomebore and Koshihikari, and those of both MWK and WBK changed only slightly in Kouiku 69 and Hatajirushi with increasing the amount of BNA. In addition, the varieties that increased the number of MWK greatly with increasing the amount of BNA tended to show a great increase in the number of panicles and grains per m2, and decrease in 1000-grain weight and percentage of ripened grains with increasing the amount of BNA. Thus, the effect of the amount of BNA on the occurrence of WIK varied with the variety, and it was suggested that the varieties with high husked rice quality under a high temperature conditions during the RP should be selected by evaluating the percentage of WBK and MWK under a light and heavy application, respectively.
