Abstract: Effect of source-sink ratio on grain filling was investigated via 18 mid-season rice hybrids with two cultural methods. The results showed that there was a high significant effect of source-sink ratio on grain filling, and the effect was mainly in the middle-lower part of a panicle, rather than the upper part of a panicle. The most sensitive index for effect of source-sink ratio on grain filling was grain plumpness index>seed setting percentage >grain filling rate. High-yield combinations with 9 t theory grain yield, 11 t potential grain yield and a seed setting percentage of 80% had the following source-sink characteristics: spikelet number 160-220 per panicle, effective panicles180×104-240×104 per hm2, 1000-grain weight 28-30 g,leaf-grain ratio 6.66-7.52 mg per grain, seed setting percentage 80%-90%, grain filling rate 96.5%-97.5%, grain plumpness index 78%-87%, grain weight 4.3-5.0 g per panicle.This study provided a scientific and practical basis for high yield breeding and cultivation of hybrid mid-season rice.

Key words: Hybrid mid-season rice, High-yield combination, Grain plumpness, Source-sink characteristic