Analysis of cool-weather damage of rice in 1993 based on data of municipalbasis in Hokkaido

Crop situation index (CSI, a ratio of yield to average yield over years) of paddy rice in the Hokkaido area in 1993 was 40, the lowest since 1949, bec ause of a cool-weather damage. The yield and CSI, however, varied largely a mong 134 municipal areas of rice cultivation in Hokkaido. The yield ranged from 10kg ha(-1) to 3,820kg ha(-1), and the CSI ranged from 0 to 68. The yi eld and CSI were highest in the northern part of Hokkaido, intermediate in the central part, and lowest in the southern and eastern parts. They tended to be lower in areas where an average yield of rice over the years was low er (r = 0. 719***). The difference in CSI between the areas was mainly due to sunshine hours and maximum air temperature from middle July to early Aug ust, although the effect on CSI was greater in sunshine hours than in maxim um air temperature. Two rice varieties, Yukihikari and Kirara 397, although bred mainly to improve eating quality, were more tolerant against cool-wea ther damage than older varieties were. We therefore considered that the wid e cultivation of these new varieties did not necessarily aggravate the cool -weather damage in 1993, although more tolerant varieties should be desirab le in the future.