Temperature rise during grain filling stage by global warming causes deterioration in rice yield and quality. This study was conducted to investigate proper panicle traits for improving grain filling under high temperature. A total of 40 Korean rice cultivars were grouped according to maturation period and exposed to high temperature during grain filling stage in greenhouse with ventilating fans. Average temperature in greenhouse was 1.1～1.5oC higher than ambient condition. Main panicle traits such as number of spikelets per panicle, number of primary rachis branches(PRBs) and secondary rachis branches(SRBs) per panicle, number of spikelets setting on PRBs and SRBs were counted after harvest and their relationship with grain ripened ratio was investigated. Grain ripened ratio under high temperature showed significant negative correlations with number of spikelets per panicle, number of total rachis branches, number of SRBs, number of total and average spikelets setting on SRBs, and ratio of number of SRBs to number of PRBs. Especially, number of total and average spikelets setting on SRBs showed highly negative correlations with ripened grain ratio, which implies grain filling under high temperature might have been more severely decreased in the cultivars with bigger sink size due to higher number of spikelets setting on SRBs.

To investigate the genetic mode of some panicle traits, interrelationships between panicle traits and ripened grain ratio, and the critical limit of panicle trait for high ripened grain ratio, four different panicle types of rice cultivars (Milyang 161, i