Poor grain growth in rice under high temperatures affected by water temperature during vegetative stage

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  • SHIMONO Hiroyuki
    Crop Science Laboratory, Faculty of Agriculture, Iwate University
  • ISHII Ayako
    Crop Science Laboratory, Faculty of Agriculture, Iwate University

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Abstract

Poor grain growth caused by high temperatures during the ripening stage is a critical problem for rice production. However, the magnitude of the reduction in grain growth also depends on the temperatures before the ripening stage. We hypothesized that the water temperature (Tw) during vegetative growth can affect grain growth under high temperatures during the ripening stage. We exposed the japonica cultivar ‘Hitomebore’ to four levels of Tw during vegetative growth, ranging from 20 to 30°C, and examined grain growth under subsequent high temperatures during the ripening stage in a 3-year experiment using plants having only main stems produced by removing all tillers. We measured green leaf area, chlorophyll content, spikelet number per panicle, hull length, and grain size. To investigate the contribution of the sink-source balance to grain growth, we examined the effect of the interaction between Tw during vegetative growth and a partial sink-removal treatment on grain weight. High air temperature during the ripening stage decreased grain weight, and low Tw during vegetative growth significantly decreased grain weight under both normal and high air temperatures during the ripening stage, without a significant interaction. The responses of grain weight to Tw during vegetative growth were observed even in plants with partial sink removal. The reduced grain growth under lower Tw during vegetative growth resulted from decreased hull length of the grains. Our results support the hypothesis that low Tw during vegetative growth can decrease grain growth in rice at high air temperatures during the ripening stage. It affects the hull size rather than the sink-source balance.

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