Simulation of heat-induced spikelet sterility in rice and evaluation of adaptation options under historical and projected meteorological conditions in Japan

Context and objective Elevated temperatures during the flowering stage can induce spikelet sterility in rice, posing a serious threat to production under climate change. Although several adaptation strategies have been proposed and are under development, their long-term performance under future climatic conditions remains uncertain. This study aimed to estimate heat-induced sterility under historical and projected meteorological conditions in Japan and to evaluate the effectiveness of three adaptation strategies: shifting flowering date, promoting early-morning flowering, and improving heat tolerance. Methods Historical and future sterility risks were assessed using gridded meteorological datasets. Future projections relied on meteorological data aligned with three greenhouse gas emission scenarios that reflect sustainable growth, middle-of-the-road development, and fossil fuel-dependent trajectories. Sterility rates under historical and projected climates were estimated by computing panicle temperature with a micrometeorological model and applying an established relationship between panicle temperature and sterility. Adaptation effects were quantified by modifying relevant parameters within the simulations. Results and conclusions Historical analyses indicated a steady increase in panicle temperature during flowering, with all scenarios showing a similar rise (+0.428℃ per decade) until around 2040. A corresponding increase in sterility rate was projected across most regions of Japan, except in the northernmost region (Hokkaido), and was closely associated with the magnitude of warming. Among the adaptation measures, modifying the heading date showed limited benefit, whereas advancing flowering time by 3 h and increasing heat tolerance by 3℃ markedly reduced sterility, even under 2050s climate conditions. The combined implementation of early-morning flowering and enhanced heat tolerance exhibited additive effects, with no indication of antagonism. By demonstrating the relative effectiveness of each strategy across future climate scenarios, this study provides important insights into the level of adaptation needed to sustain rice production. Significance This study offers an early evaluation of heat-induced sterility risks in rice under historical and future climates in Japan, before the issue becomes widespread. By quantifying the effectiveness of major adaptation strategies, the results provide useful guidance for breeding programs seeking to develop heat-tolerant cultivars in anticipation of continued warming.