Abstract
The varietal differences in the effects of high temperature and high humidity on the spikelet fertility of japonica rice cultivars were investigated. We constructed an apparatus that could control air temperature and humidity simultaneously in a chamber placed in a paddy field. We examined the effects of 59%, 72%, and 88% relative humidity at 35°C air temperature on fertility percentage and the amount of pollen shed on the stigmas among four cultivars (Koganebare, Hinohikari, Sasanishiki, and Hitomebore). The fertility percentages of each cultivar declined under a high humidity of 88%, and this trend differed among the cultivars. In Koganebare and Hinohikari, the degree of decline was large. The percentage of spikelets with few pollen grains on the stigmas increased with the increase in relative humidity. This tendency was striking in Koganebare. Under high humidity at 31°C, a varietal difference was observed in pollination but not in fertility percentage. Thus, the effect of humidity on the high temperature–induced sterility varied with the cultivar. The fertility was lower in the cultivars in which the percentage of spikelets with only a few pollen grains on the stigmas was more increased by a high humidity condition.
