In this study, two experiments were conducted to investigate the mechanism of high temperature-induced sterility at flowering in rice plants, comparing the varietal differnces in occurrences of sterility. Six rice varieties were used ; Nipponbare, Koshihikari, Asahi, Coloro 2, Brirish Honduras, and Milyang 23.
The results obtained were as follows ;
1. There were considerable differences among varieties in the peak time of spikelets opening during the day, under the condition of high temperature (39℃).
2. The spikelets of Milyang 23 opened 2 hours or more earlier than those of the other varieties, and about a third of spikelets had flowered in the condition before the treatment of 39℃. The advancement of spikelets opening time would be contributed to avoidance of the sterility induced by high temperature. The percentage of ripened grains in this variety was 7.7% in the 39℃ treatment for 6 hours, whereas, in other varieties, it was in a range of 0-2%.
3. The most spikelets of British Honduras opened under 39℃ treatment. In this variety, the number of full ripened grains were extremely decreased, and the most of nonripened grains were not fertilized. As a smal number of pollen grains were observed on the stigma, the dehiscences of anthers would be incomplete, and pollens would not be shedded mostly under high temperature treatment of 39℃.
4. In Japonica varieties including Coloro 2, many spikelets opened at the time just after the 39℃ treatment. However, there were many imperfectly ripened grains, which would not develop during about 6 days after anthesis. Although many spikelets of Japonica varieties did not opened under 39℃ treatment, the dehiscences of anthers were seemed to be inhibitted by a high temperature before anthesis. Therefore, the percentage of ripened grains would be decreased in the 39℃ treatment.