Yearly Variation of Panicle Characters in Japonica Rice (Oryza sativa L.)

This study was conducted to determine the effect of nitrogen level and yearly variation of panicle traits, and to examine the desirable panicle structure for better ripening and higher yield. Four rice varieties having different panicle types were transplanted under two different nitrogen levels in 2002 and 2003. There were more primary rachis branches (PRBs) per panicle and grains setting in Sindongjinbyeo and Iksan#467, but secondary rachis branches (SRBs) per PRB was fewer than in Saegyehwabyeo. While Dongjin#1 and Saegyehwabyeo revealed more grains setting on SRB and lower ripened grain ratio. It was desirable for enhancing ripened grain ratio to increase the number of PRB and mean grains setting on PRB per panicle rather than the number of SRB or the number of grains per SRB setting on PRB. Therefore, grains setting on PRB, mean number of SRB per PRB and mean grains setting on SRB per PRB were main panicle traits closely associated with ripened grain ratio. The number of unfertile PRB per panicle was negatively correlated with ripened grain ratio. These indicate that the establishment of sink capacity should be attained through increase of number of PRB, and decrease of the number of unfertile PRB per panicle. Variety×year was the significant sources of variation for PRBs and SRBs per panicle. Results show that ripened grain ratio was affected by PRB and SRB factors. Therefore, increasing the yielding potential of variety needs more number of primary rachis branches per panicle.