Abstract
To clarity the physiological and ecological characteristics of high yielding varieties in rice plants, the yield, its components and the process of dry matter production were compared between the cultivar Akenohoshi, a new high yielding variety, and the cultivar Nipponbare, a Japanese standard variety. The yield was 170kg/10a higher in Akenohoshi than that in Nipponbare due to higher dry matter production and larger spikelet number per unit area in Akenohoshi with larger panicles compared with those in Nipponbare. The process of dry matter production was examined by growth analysis method. The crop growth rates were higher at all stages and especially much higher at the ripening stage in Akenohoshi owing to higher net assimilation rates as compared with those in Nipponbare. Leaf area indices at the panicle formation and ripening stages were not different significantly between the two varieties. Net assimilation rates were affected by the canopy structure related to leaf arrangement and photosynthetic rates of leaves in the canopy. As the light extinction coefficient at the panicle formation and ripening stages was not significantly different between the two varieties it was assumed that the difference in the net assimilation rates between the two could be due to the difference in the photosynthetic rates of leaves in the canopy. Furthermore, the process of dry matter accumulation in the panicle was compared and was discussed from the point of the senescence of the panicle.
