Controlled soil drying mitigates the effects of high-temperature stress on rice quality by enhancing starch accumulation and stabilizing starch structure and functional properties

Effective water management is essential for addressing high-temperature (HT) challenges to rice quality. This study explored whether a controlled moderate soil drying (MD) regime could serve as a viable alternative to the conventional well-watered (WW) regime in mitigating the effects of HT stress on rice quality. Two rice varieties were cultivated under normal temperature and HT conditions and subjected to the WW and MD regimes during the grain filling period. Findings revealed that HT stress significantly compromised rice quality. However, under HT conditions, the MD regime proved more effective than the WW regime in maintaining plant water homeostasis and enhancing photosynthesis. This improvement not only facilitated the accumulation of nonstructural carbohydrates in the grains but also boosted the activity of key starch-synthesizing enzymes, leading to a marked increase in starch accumulation. Specifically, under HT stress, the MD regime significantly enhanced the milling and appearance quality of rice; for instance, the head rice rates of Jinxiangyu-1 and Yangdao-6 increased by 13.6 % and 13.7 % while their chalkiness degrees decreased by 26.2 % and 24.8 %, respectively. Moreover, the MD regime contributed to the stabilization of starch molecular structure and functional properties, thereby further alleviating the negative impacts of HT stress on rice quality.