Green manure enhances reproductive heat resilience by cooling panicles and endosperms at grain filling in a heat-resilient cultivar Nijinokirameki

Although our previous work showed that green manure can lessen ripening heat damage in the widely grown but heat-susceptible Japanese cultivar Koshihikari, it remains unclear whether similar benefits occur in heat-resilient cultivars and how green manure influences source–sink molecular responses during ripening.

Here, using the heat-resilient cultivar Nijinokirameki, we tested whether green manure alleviates ripening heat stress by modifying panicle thermal status, nitrogen assimilation, and early endosperm stress responses. Green manure increased flag-leaf size and tiller (panicle) number and enhanced ripening-stage heat resilience by lowering panicle temperature without a meaningful phenological shift. Consistent with reduced heat load at the target organ, endosperm RNA-seq at 5 days after flowering (DAF) revealed weaker induction of heat-responsive programs under green manure, accompanied by increased grain protein content and reduced chalkiness classes (e.g., white milky, and white belly and back kernels).