抄録
Varietal characteristics of the rice car at filling period were examined (Table 1). The increasing process of ear weight after ear emergence, which draws a sigmoid curve (Fig. 1), is consisted of three phases differing in increasing rate of ear weight. Increasing rate of ear weight at the maximum increasing period (LIP in Fig. 1), when dry weight of straw decreased rapidly, tended to be larger in large grain and indica varieties than in japonica varieties. The period itself however, was longer in large grain and Japonica varieties than in indica varieties. Contribution ratio of dry weight increased during LIP to final ear weight was 50 to 80% in most of materials used, although some indica varieties showed small contribution ratio below 50%. Increasing rate of ear weight at LIP correlated positively with final ear weight (Fig. 2 and Table 2). Both final ear weight and increasing rate of ear weight at LIP tended to be smaller in japonica varieties than in others. Therefore, it would be indicated that the large sink size of large grain and indica varieties originating from the potential capacity (grain size×grain number) developed before heading may have caused the rapid translocation of assimilates and resulted in the heavy final ear weight. Decrease of straw weight at LIP would be due to translocation of assimilates stored in the straw before heading time. Decreasing rate of straw weight at LIP correlated positively with increasing rate of ear weight at the same period (Fig. 3 and Table 2). Ear weight of large grain varieties, however, tended to increase more rapid than that of japonica varieties at the same levels of decreasing rate of straw weight, indicating that in large grain varieties translocation of assimilates produced newly may have occurred during LIP in addition to the assimilates stored in straw before heading.
