Effect of light intensity on grain quality of rice at different spike positionsduring grain-filling stage

Light intensity is an important ecological factor that greatly influences rice grain formation and quality. This study discussed the effects of light intensity on rice quality at grain-filling stage and the differences in variety types and spikelets at different panicle positions. To do this, two pot-grown super rice cultivars, "Yangliangyou 6" (indica) and "Wuyunjing 23" (japonica), were subjected to three light intensity treatments (71%, 55% and 40% of normal light intensity respectively) at post-anthesis grain-filling stage, with normal outdoor growth as the control. The study aimed to throw more light on the physiological mechanisms of rice grain formation to lay the theoretical basis for improved rice quality. The results suggested that light intensity during grain-filling greatly influenced rice quality. Compared with the control, rice grain quality under the three treatments worsened with the weakening of light intensity. Grain quality response to light intensity varied with light intensity degrees, variety genotypes and grain positions on rice panicles. While grain quality on spikelets with late flower formation was poorly stability, that on spikelets with early flower formation was relatively stable. Milled rice and rice amylose content decreased and chalkiness increased with the weakening of light intensity. Amplitude change in grains on primary tillers was relatively larger than in grain on secondary tillers. Also the weaker the light intensity, the lower was the breakdown value, the higher were the setback value and crud protein content, and the worse were the rice cooking and eating qualities. Reasonable sowing times based on variety type and scientific cultivation practices for improved light conditions and rice growth likely mitigated any negative impacts of low light intensity on rice quality.