Varietal Difference in Panicle Traits as Affected by Nitrogen Level and Planting Density in Japonica Rice

Abstract

This study was carried out to investigate the effect of nitrogen level and planting density on panicle traits and to examine the desirable panicle structure for better ripening and high yielding in rice. Four different panicle types of rice varieties such as Sindongjinbyeo, Dongjin #1, Saegyehwa and Iksan 467 were transplanted under three different nitrogen levels and two different planting densities. Sindongjinbyeo and Iksan 467 revealed more primary rachis branches (PRBs) per panicle and more grains setting on PRB, but fewer secondary rachis branches (SRBs) per PRB and fewer grains setting on SRB per PRB. Consequently, they showed fewer unripened grains setting on SRB and also higher ripened grain ratio, while Dongjin #1 and Saegyehwa 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 the main panicle traits closely associated with ripened grain ratio in rice. High ripened grain ratio over 90% was obtained by controlling the PRBs over 11.5 per panicle, the mean grains setting over 67 per PRB, the number of SRBs fewer than 20 per panicle, and grains setting on SRB fewer than 60 (i.e. mean number of branches or grains fewer than 1.7 or 5 per SRB, respectively.). In order to increase the sink capacity per panicle with higher ripening quality, it would be desirable to increase the number of PRB per panicle and number of spikelets per PRB in the present source capacity in japonica rice.