Abstract
Average rice grain weight decreases under a high night temperature condition, and the quality of rice grain becomes poor under either high night or high day temperature condition. The effects of exposing either panicle or vegetative parts to a high temperature on the grain weight and the rice grain quality were investigated. Three temperature conditions used were ; high night temperature (day/night : 22/34 °C), high day temperature (34/22 °C) and control (22/22 °C). The average grain weight decreases were 7–11% by exposing the whole plant to a high night temperature and 5–6% by exposing the panicle to the high night temperature, but it was not influenced by exposing the vegetative parts to a high night temperature. The average grain weight did not correlate with the whole plant weight (r=0.241). These results suggest that the decrease in average grain weight under a high night temperature is not caused by the deficit of carbohydrates in the leaves and the culms due to increased respiration loss. The grain quality became poor by applying either high night or high day temperature to the panicles as well as to the whole plants. It was assumed that the decrease in grain quality under high night temperature condition was not due to the deficit of carbohydrates in the leaves and the culms because exposure of the vegetative parts to this temperature condition did not decrease the grain quality.
