Effects of high temperature and early drainage on leaf CO₂ assimilation and grain yield in the rice cultivar Hinohikari

Abstract

In western Japan, rice grain damage from high temperatures has recently been severe. The adverse effects of high temperature on rice ripening can be accentuated by water management practices. In field experiments carried out under different weather conditions, the early drainage decreased yield, grain weight, and quality in 2008, but early drainage had no effect on brown rice yield in 2009 or 2010. Decreases in grain weight, yield, and the percentage of perfect grain in the dry regime in 2008 compared with the wet regime of the years can be explained by the early drainage during the early grain-filling period. In 2010, the mean daily temperature averaged over the 20 days after heading was 29°C, and the percentage of perfect grains was low. The combination of high temperature and abundant radiation during the grain-filling period may explain the low proportion of perfect grains without a decrease in grain weight in 2010. The effect of drainage was smaller in 2010, when the high temperatures caused rapid senescence and shortened the grain-filling period. Thus, grain filling may have been completed before the water shortage could reduce the availability of CO₂ to a critical level.