Numbers of degenerated and surviving spikelets associated with the number of differentiated spikelets among various rice [Oryza sativa] cultivars

Spikelet differentiation is the basis of spikelet survival in rice. However, information about the number of differentiated and degenerated spikelets and their relationship with the number of surviving spikelets among various cultivars is lacking. Chinese hybrid indica, indica and japonica cultivars were used for the experiments. Instead of estimating the number of degenerated spikelets based on the number of remaining degenerated branches, the number of degenerated spikelets was counted under the microscope. The number of differentiated spikelets per panicle varied substantially, mainly due to the changes in the number of differentiated secondary branch (SB) spikelets. With the increase in the number of differentiated spikelets per panicle, the number of degenerated spikelets increased more rapidly than that of the surviving spikelets. As a result, the percentage of surviving spikelets decreased. The number of degenerated spikelets was derived mainly from the degenerated SB of surviving primary branch (PB). The percentage of degenerated spikelets was negatively correlated with the ratio of shoot dry weight (SDW) to the number of differentiated spikelets. Dry matter accumulation at heading was more important for increasing the number of surviving spikelets per panicle than the ratio of the number of surviving spikelets to SDW. Only cultivars with both a higher SDW and larger ratio of the number of surviving spikelets to SDW could produce a larger number of surviving spikelets per panicle. We concluded that with the increase of the PB number per panicle, the number of differentiated spikelets would increase substantially. Increasing the dry matter accumulation relative to the number of differentiated spikelets may result in the decrease of the percentage of degenerated spikelets and increase of the number of surviving spikelets per panicle