Comparison of the occurrence of kernel damage in rice plants grown in a heated greenhouse and in a paddy field of high temperature year

The percentages of the number of heat-damaged kernels, white-back or basal-white kernels and milky-white kernels in a heated greenhouse were compared with those in a paddy field in a high-temperature year to examine whether the greenhouse observation could represent the varietal difference in the tolerance to the damages in the field condition. Twelve varieties of rice, considered to have various degrees of tolerance to kernel damage due to high temperature, were cultivated in the greenhouse on benches (70cm high, 15cm deep) filled with paddy field soil. The plants were exposed to high temperatures of 27.6similar to28.3degreesC (day/night temperature : 29.7similar to30.1degrees0/25.3similar to26.3degreesCX) during the period from heading to maturity. At maturity, the percentages of white-back or basal-white kernels and milky-white kernels were counted in eight plants of each variety. A significant difference (P < 0.05) in the percentage of occurrence of white-back or basal-white kernels was recognized among varieties exposed to high temperatures in the greenhouse. There was a significant positive correlation between the occurrence of these kernels in the greenhouse and in the paddy field in 1999 when high-temperature days continued during summer. There was no significant varietal difference in the occurrence of milky-white kernels. These results suggested that the percentages of white-back and basal-white kernels were appropriate indicators and the tolerance to high temperature. We proposed that five varieties, Koshijiwase (resistant), Kokoromachi (moderately resistant), Akitakomachi (moderate), Hitomebore (moderately sensitive) and Hatsuboshi (sensitive) could be the indicator varieties to the tolerance.