以同一穗上弱势粒占强势粒千粒重的百分比表示籽粒相对充实度。2003－2004年在大田条件下，通过喷施植物生长调节剂，研究了籽粒灌浆、充实度和相对充实度的动态，探讨了籽粒相对充实度化学调控及其与水稻产量和品质的关系。结果表明，灌浆速率在灌浆初期（花后5～12 d），强势粒平均比弱势粒高256%；而在灌浆盛期（花后12～19 d）及后期（19～32 d），弱势粒平均分别比强势粒高16.67%、154.55%。PR1处理可明显促进弱势粒的起始灌浆速率，及早启动弱势粒的灌浆。籽粒相对充实度在花后5～12 d迅速降低，花后12～19 d迅速上升，花后19～32 d缓慢上升，呈先降后升的偏“V”型动态曲线。PR1处理在花后19 d籽粒相对充实度明显高于对照和其他处理。灌浆中、后期（花后19～32 d）的籽粒相对充实度基本上与平均千粒重、经济系数、理论产量和实际产量呈显著或极显著正相关，与强势粒和弱势粒的垩白粒率、垩白面积、垩白度呈显著或极显著负相关，与弱势粒的糙米率呈显著正相关，花后19 d的相对充实度与弱势粒的精米率、整精米率呈显著正相关。
The poor grain plumpness is the general question in modern large panicle rice cultivars. The relationship of grain plumpness with grain yield and grain quality has not been reported. The field experiment was conducted in 2003–2004 to research the dynamic changes of grain filling rate, grain plumpness, relative plumpness and their relationship with grain yield and grain quality using the rice cultivar of Yujing 6 with chemical regulation treatments of T27, T23, PR1 and T30 (the check is water) at 5 days before heading. The grain relative plumpness is expressed by the percentage of 1000-grain weight of inferior grains to superior grains in one panicle of rice. The result indicated that the super-grain filling rate was 256% more than that of inferior-grain at early grain-filling stage (5–12 days after heading), and the filling rate of inferior-grain was 16.67% and 154.55% more than that of super-grain at mid-filling stage and later-filling stage respectively. The dynamic changes of grain plumpness and 1000-grain weight in superior grain were also different from those in inferior grain. The grain relative plumpness reduced rapidly at 5–12 day, rose rapidly at 12–19 days and rose slowly at 19–32 days after heading. The grain relative plumpness of PR1 treatment was higher than that of CK and other treatments obviously. There were significant positive correlation at P=0.05 or P=0.01 between grain relative plumpness and mean 1000-grain weight, economic coefficient, theoretical yield and true yield, brown rice percentage of inferior-grain, significant negative correlation at P=0.05 or P=0.01 between grain relative plumpness at 19–32 days after heading and chalky percentage, chalky area, chalkiness, and significant positive correlation between the grain relative plumpness at 19 days after heading and milled rice percentage, head rice percentage of inferior-grain. The results suggest that the Grain relative plumpness is a suitable index to express the relationship between super grain and inferior grain in one panicle.
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