Effect of high temperature on ripening in rice plants - Comparison of the effects of high night temperatures and high day temperatures

The effects of high-temperature stress on rice ripening is well documented. However, it is unclear which is more effective on rice ripening, high night temperature (HNT) or high day temperature (HDT). In this study, the effects of HNT (22/34degreesC; day/night temperature) has been compared with those of HDT (34/22degreesC), with a control (22degreesC continuously or 28/20degreesC; max/min temperature) under growth cabinets. The average grain weight decreased under HNT compared with that of control, but it was not affected under HDT. On the other hand, the percentage of normal (undamaged) grains decreased not only under HNT, but also under HDT. Furthermore, the decreases in grain weight and grain quality took place in spite of the grain position in a panicle. The indicator of grain volume (length X width x thickness) correlated with the grain weight. Under HNT, grain width and thickness both decreased; under HDT, grain width decreased, but thickness increased. These results suggest that the decrease in grain width and its thickness affected the grain weight decreases under HNT, whereas under HDT the grain weight remains stable because the loss of width would be fully compensated for by increases in its thickness.