Abstract:

To explore the effects of high-temperature and drought combined stress on the yield and physiological characteristics at heading and flowering stage of mid-season rice, and to determine the meteorological disaster threshold, this study used Jingzhou’s main indica hybrid rice variety, ‘Shuangliangyou 138’, as the experimental material. The experimental treatments included a control group (CK), high-temperature group (T), drought group (D), and combined high-temperature and drought stress group (T-D). Through the artificial simulation of stress conditions, the study analyzed the impacts of different stress levels on rice yield and physiological traits, and identified the meteorological disaster indicators and thresholds. A composite disaster evaluation model based on meteorological factors was established. Results showed that the high-temperature and drought combined stress had a significant greater inhibitory effect on rice yield and physiology than single stress, with more pronounced effects under normal sowing dates (phase II) than delayed sowing dates (phase IV). Compared to the CK group, the T-D treatment led to a 70.36% decrease in grain yield, with a reduction in total grain number per panicle, seed setting rate, and 1000-grain weight by 40.53%, 53.05%, and 19.43%, respectively, SPAD value decreased by 12.3%, indicating a synergistic enhancement effect between high temperature and drought. Path analysis showed that during the heading and flowering stage, the effect of high-temperature and drought combined stress on rice yield was most significantly influenced by seed setting rate, followed by total grain number per panicle, SPAD, 1000-grain weight, panicle length, and effective panicle number, and the seed setting rate was identified as the most sensitive yield factor and served as the key disaster indicator. The meteorological disaster threshold for this indicator was found to be a high-temperature thermal accumulation of 80.8℃·d and a 20 cm soil relative humidity of 34.4%. A composite disaster evaluation model based on high-temperature thermal accumulation and soil moisture was established, revealing that high-temperature stress contributed more to the yield loss than drought, and high temperature exacerbated the effects of drought. This research provides the technical support for the monitoring, early warning, and risk assessment of high-temperature and drought combined disasters in rice cultivation.

Key words: mid-season rice, heading and flowering stage, high-temperature and drought, seed setting rate, meteorological disaster threshold