Impact of Heat Stress on Pollen Fertility Rate at the Flowering Stage in Korean Rice (Oryza sativa L.) Cultivars

Rice is very sensitive to high temperatures during the reproductive stage, particularly during the flowering and anthesis periods. To determine how high temperatures result in sterility during the flowering period in Korean rice cultivars, groups of 11 cultivars were subjected to different temperature regimes (24, 28, 30, and 33°C) during the flowering stage using sunlit phytotrons. At an average of 33°C, all 11 rice cultivars reached anthesis earlier than at the other temperatures. Microscopy analyses revealed significant differences in pollen germination and pollen viability in cultivars grown at 33°C compared to those cultured at lower temperatures. At 33°C, the cultivars had significantly lower fertility rates (47% reduction) than cultivars grown at 24°C. These findings are important as rice pollination and fertility depend on the pollen viability and germination. The present study shows that rice fertility is negatively affected by excessively high temperatures.