Genotypic variation in the response to high water temperature during vegetative growth and the effects on rice productivity under a cool climate

Abstract

We examined the effects of high water temperature (Tw) during early vegetative growth on dry matter production, grain yield, and grain quality in a 2-year field trial in northern Japan using two rice cultivars: ‘Hitomebore’, a standard cultivar for this region, and ‘Koshihikari’, a late-maturing cultivar. The heading date of ‘Koshihikari’ was 8–9 days later than that of ‘Hitomebore’. Heading date was significantly earlier for both cultivars (by 2–5 days) in the high Tw treatment, without a significant cultivar×Tw interaction. High Tw significantly increased dry matter production before heading, and there was a significant cultivar×Tw interaction: ‘Koshihikari’ responded more than ‘Hitomebore’ to high Tw. This genotypic difference was explained by the daily rate of dry matter increase rather than by the growth duration. After heading, leaf senescence measured as the reduction of the SPAD value was greater at high Tw for both cultivars. Radiation-use efficiency after heading was significantly reduced by high Tw for both cultivars. Consequently, the positive effect of high Tw on dry matter production was reduced for both cultivars at harvest. Grain yield was significantly increased by high Tw (by 1–20%), but without a significant Tw×cultivar interaction. These results suggest that to increase grain yield above that for the standard cultivar ‘Hitomebore’, manipulation of the accelerated leaf senescence caused by high Tw will be a key factor in efforts to adapt rice to future global warming.