Abstract: In pot experiments of inter-subspecific rice hybrid Shanyou 413, higher level of IAA in rice plants, through IAA solution injected to the boot of the rice plant at booting stage, had little effect on the average weight and seed-setting of the superior grains located on the distal part of the panicle, nevertheless, significantly inhibited the filling of the inferior grains positioning on the secondary branches, which resulted in a longer "quiescent spell" before the beginning of the inferior grain filling and slower rate of the ovary expansion of the inferior grains. Consequently, the average weight and seed-setting of the inferior grains in treated plants was reduced to a large extent. Moreover, application of IAA to plants before heading promoted the abortion of the inferior florets. After heading, 3 top primary branches were clipped off and 20 μL lanoline, containing different quantities of IAA 0, 10 , 20, 30 and 40 ng/μL, were smeared onto the apex of the panicle axis. The results showed that clipping and only lanoline smeared decreased unfilled and partially-filled grain (UPG) percentage of the inferior grains on the secondary branches of the 3 base primary branches from 47.7 % of check to 8.2%. However, when the clipping and IAA applied, the UPG percentage was nearly restored to the level of check except the highest IAA quantity used, which indicated that as the influence on the filling of the inferior grains was concerned, IAA was able to substitute for the superior grains. It is deduced that the superior grains inhibit the filling of the inferior grains by the "apex dominance". When the inhibition occurs, the inferior grain filling can not be improved though the assimilate supply is quite rich. In field yield test of 1993-1994, uniconazole was proved to increase yield of intersubspecific rice hybrid Xieyou 413 and Shanyou 413 in advantage of above 10% to check, by ameliroating the filling of the inferior grains and resulted higher seed-setting. The possibility for fulfillment of the highest yieldingpotential in inter-subspecific rice hybrids is also discussed.

Key words: apex dominance , indole acetic acid , inferior grains, intersubspecific hybrid rice , superior grains, uniconazole

摘要： 以亚种间组合汕优413和协优413、籼型杂交组合汕优10号为材料进行研究。结果表明对弱势粒灌浆的影响，IAA具有代替强势粒的作用。即使剪去顶端3个一次枝梗、营养物供应非常充足，由于IAA的存在，弱势粒的灌浆也较为迟缓，最终形成大量空秕粒，与不修剪的对照接近，说明弱势粒的灌浆主要受IAA调控，也证明强势粒以“顶端优势”的方式抑制弱势粒的灌浆。

关键词: 顶端优势, 吲哚乙酸, 强势粒, 弱势粒, 烯效唑, 亚种间杂交水稻