New insights into rice phenology: discovering the effect of insolation on heading response.

Precise growth management is required for climate-smart and sustainable crop production in response to climate change, with the heading stage being the most important. Research on the control of heading in rice (Oryza sativa) has mainly focused on day length and temperature; however, research on the effects of insolation is limited. Therefore, this study analyzed the differences in rice growth and heading responses under different light intensity and temperature conditions. Five early-maturing and seven medium-late-maturing rice varieties were used for each japonica heading ecology type. Our results showed that leaf age development, an indirect measure of rice phenological development, was inhibited under low light intensity and low-temperature conditions. Accordingly, the heading date was also delayed by approximately 18 days at low temperatures and 21 days at low light intensity, with no difference among ecotypes. We also found an interaction between temperature and light intensity, with the light intensity-mediated delay in heading date being affected more by high temperatures. This study demonstrated that light intensity and temperature have a major effect on heading date variation, suggesting that the impact of insolation must be considered for the accurate prediction of heading stage variation. These results could shed new light on rice phenology research and contribute to the implementation of precision agriculture.