Grain‐filling response of winter wheat (Triticum aestivum L.) to post‐anthesis shading in a humid climate

Abstract To assess the impacts of clouds during the grain‐filling period on the leaf senescence and yield of wheat (Triticum aestivum L.), we conducted a 4‐year plot shading experiment in a well‐drained Andosol in northern Japan. Plants were shaded after the beginning of anthesis in mid‐June, which corresponds to a naturally cloudy period in the study region. The effect of shading depended on its synchronization with soil drying, which affected leaf senescence. Grain yield was determined by solar radiation at the beginning of the grain‐filling period, except in 2015, which was a dry year. Later anthesis in 2016 and 2017 significantly reduced the number and weight of individual grains in the shading treatments. Moreover, “Kitahonami”, with late anthesis, showed a significantly slower increase in the individual‐grain weight during the grain‐filling process after shading than “Yumechikara”. When the duration between anthesis and shading was short, shading significantly reduced the number and weight of grains, and later anthesis makes it more likely that regional reduced light levels are encountered, resulting in fewer grains; the sensitivity of individual‐grain weight to shading synchronized with an increase in grain protein contents. Our results suggest that in wet years, later anthesis makes it easier to encounter regional reduced light and fewer grains; in addition, insufficient light limits photosynthesis under shade and decreases yield.