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

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 (T w ) during vegetative growth can affect grain growth under high temperatures during the ripening stage. We exposed the japonica cultivar 'Hitomebore' to four levels of T w during vegetative growth, ranging from 20 to 30℃, 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 T w during vegetative growth and a partial sink-removal treatment on grain weight. High air temperature during the ripening stage decreased grain weight, and low T w 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 T w during vegetative growth were observed even in plants with partial sink removal. The reduced grain growth under lower T w during vegetative growth resulted from decreased hull length of the grains. Our results support the hypothesis that low T w 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.

Yield and biomass under the different water levels on three Japonica rice cultivars

“…We found that large leaf areas couldn't generate a high yield. Probably, the green leaf area did not respond consistently to water temperature during vegetative growth and photosynthetic capacity would not increase under higher Tw during the vegetative stage [16]. So, the low yield on HH indicates the effect of high temperature in the process of supplying carbohydrates from leaves to grains.…”

“…We can see in Table 1 shows the heading stage on HH is faster than NM and HR, so the grain on HH is exposed to high temperatures. In terms of carbohydrates, water temperature during the vegetative stage [16] and sunlight during ripening [17] will affect seed growth. Moreover, grain growth during the ripening period is determined by the size of the hull and by the supply of carbohydrates to the grain, as well as the use of these carbohydrates [16].…”