Comparison of grain filling characteristics of various rice varieties (combinations).

Further improvement in rice grain filling depends,to a large extend,on our understanding on the physiological and biochemical processes of grain filling in rice.The characteristics of grain filling were analyzed by Richards Equation,using inter-subspecies hybrid rice combinations,Liangyoupeijiu,intervarietal hybrid rice,Shanyou 63,and conventional rice,Wuyujing 3,as experimental materials.For variety with good grain filling,the differences in the initial growth potential,maximum grain filling rate and mean grain filling rate were not obvious between superior grains and inferior grains.Grain filling processes of superior and inferior grains appeared to be in a synchronous pattern.However, significant differences were observed in grain filling characteristics between superior grains and inferior grains for variety or combination with poor grain filling.These results implied that the main causes of poor grain filling were the later filling initiation and lower filling rate of inferior grains.Furthermore,the sucrose content in inferior grains was higher than that in superior grains of the combinations with poor grain filling at the early and mid grain filling stages, which indicated that the major restricting factor of grain filling was not the supply of assimilates,but physiological activities of sink.