Influence of the temperature during grain filling stage and nitrogen application rate on yield and quality of indica hybrid rice

Context: Climate change threatens rice production by increasing the frequency of extreme temperatures during grain-filling stage (TGF). Nitrogen application can significantly affect rice yield and quality. However, the effects of interaction between TGF and nitrogen application rate on yield and quality of rice remains unclear. Objective: The objectives of this study were to comprehensively evaluate the quantitative regulatory mechanism between TGF and nitrogen application rate on rice yield and quality formation. Methods: A two-year field experiment with three varieties, five sowing dates, and three nitrogen application rates was conducted at four ecological sites in the middle and lower reaches of the Yangtze River, China in 2019 and 2020. Grain yield, milling, appearance, and eating quality were quantified for each treatment. Results: This study demonstrated that TGF varied from 17.8 degrees C to 31.4 degrees C in different sites and sowing dates and decreased by an average of 2.1 degrees C for every 15 days the sowing date was delayed. The grain yield, head rice rate, chalky grain rate, chalkiness and taste value were all related to TGF through a quadratic function. The optimum TGF for both yield and quality of indica hybrid rice was 24.2-26.5 degrees C. In terms of grain yield, nitrogen agronomic efficiency increased linearly with TGF, and nitrogen application could only confer a small increase in yield or even reduce yield under extreme low TGF. Nitrogen application alleviated the adverse effects of high TGF on rice quality, but exacerbated the deterioration of quality under low TGF. For milling and appearance quality and eating quality, the critical TGF leading to such opposite regulatory effect were identified as 23.4 +/- 0.4 degrees C and 29.5 +/- 0.5 degrees C, respectively. The variations of the ratio of amylopectin to amylose and protein content altered texture and starch gelatinization properties, mainly explaining the differences in eating quality caused by TGF and nitrogen application rate. Conclusions: The present study suggests that TGF should be considered when formulating nitrogen management strategies for high-quality rice, which is crucial for alleviating the deterioration of rice quality caused by extreme TGF under global climate change.