Evolution Characteristics of Grain Yield for Mid-season Japonica Rice Cultivars

In this study,11 japonica rice cultivars ( including hybrid combinations) applied in the production in Jiangsu Province during the last 50 years were used as materials. All the test cultivars were field grown and the evolution characteristics of grain yield was investigated. The main results are as follows: Grain yield was progressively increased with the evolution of the cultivars. Increase in grain yield was attributed mainly to the increase in total number of spikelets,and increase in spikelets resulted mainly from large panicles. Hybrid rice had lower percentage of field grains,which limited its high-yielding potential. From old cultivars to modern hybrid rice,biomass and harvest index were simultaneously increased,and the biomass,especially after heading,was increased more relative to the increase in harvest index. Total leaf area index ( LAI) ,LAI of productive tillers and LAI of top three leaves at the heading stage were significantly increased with the evolution of the cultivars. Increase in spikelets,however,was more than that in leaf area,which resulted in the increase of grain-leaf ratio ( the ratio of total spikelet number to leaf area at heading) . LAI,root weight and root activity of modern cultivars were much greater than old cultivars at each growth stage. However,senescence in leaves and roots at the late grain filling stage was earlier for modern cultivars than for old ones,which may limit photosynthetic productivity of modern cultivars.