Abstract

1. Three daylength sensitive rice varieties, Shinriki, Shuang-chiang and Wan-tze were subject to the short day treatment of 9L+15D. During the 15D period, they were placed at the following temperature level :15°,20°,24°,28°C and 32°C. It was found that all three varieties failed to head at the night temperature of 15°C. The optimum night temperature was 24°C up to 28°C for Shinriki and 28°C for Shuang-ching and Wan-tze. At temperature lower or higher than the above, heading was delayed. 2. A daylength insensitive variety Norin No.11 with a very short growth period was subject to the following night temperature level: 15°,20°,24°,28°,32°and 34°C. It was found that low temperatures suppressed floral bud initiation and the growth of floral buds already initiated. However, there was still heading at 15°C. 3. The author express doubts about the temperature sensitivity indicators of rice varieties as suggested by Japanese investigator.