Genotypic Variation in Rice Cold Tolerance Responses during Reproductive Growth as a Function of Water Temperature during Vegetative Growth

We examined genotypic variation in the effect of rice ( Oryza sativa L.) responses to water temperature ( T w ) during vegetative growth on cold tolerance during reproductive growth in pot and field experiments. Cold tolerance was evaluated based on the percentage spikelet sterility induced by a cool and deep irrigation treatment during the reproductive growth phases. In the pot experiment, rice plants from two cultivars with different cold tolerance were exposed to different levels of T w during vegetative growth and their cold tolerance was tested. Spikelet sterility of both cultivars decreased with increasing T w during the vegetative growth phase for temperatures ranging from 19 to 30°C, with parallel lines for the regression equations for sterility as a function of temperature (a slope of 4.0% per 1°C) for both cultivars, although the y ‐intercepts differed by 38% points between the cultivars. In the field experiment, four rice cultivars were grown under two levels of T w during vegetative growth, and their cold tolerance was tested during reproductive growth at two locations (Miyagi Prefecture and Aomori Prefecture in Japan). We found that spikelet sterility decreased at high T w during vegetative growth for all cultivars and locations. Our results suggest that high T w during vegetative growth can improve cold tolerance during reproductive growth for the tested cultivars without a significant cultivar × T w interaction.