水稲幼穂形成期前後の温度処理が一穂頴花数の増減と不稔発生に及ぼす影響

抄録

Influence of the temperature treatments before and after the growth stage of panicle formation on the number of spikelets per panicle and the sterility of grains were examined under the controled environments for several rice cultivars which had different local adaptability. The results obtained are summerized as follows : 1. Plant height was increased in every cultivar as the temperature (of the growth period) before the panicle formation stage increased. The increasing rate in Shiokari, cultivar adapted to cold district of Japan, was twice as high as that in Harima, cultivar adapted to the warm district of Japan, under the high temperature condition. Number of tillers, on the contraly, decreased in accordance with the increase in temperature in each cultivar. Among those the rate of depression in high temperature was remarkable in Harima. 2. Number of spikelets attached on the primary rachis-branches was increased by the high temperature treatment in the growth period prior to the panicle formation satge in each cultivar. The efect of any temperature treatment after the panicle formation stage on it was not recognized. 3. As the temperature in the growth period before the panicle formation stage increased, the sterility of grains was decreased in Shiokari. In the cultivar Harima, however, the sterility of grains decreased with decreasing temperature. 4. Difference in number of spikelets per panicle by the differential temperature treatments was governed primarily by the difference in the number of degenarated secondary rachis-branches caused by the treatments. 5. It was recognized that the low temperature treatment in the growth period after the panicle formation stage did not result in the increase in sterility of grains, but the treatment brought about the increase in the number of the degenerated secondary rachis-bran-ches in Shiokari which has been considered to be one of the cold tolerant varieties cultivated in the northeastern cold district of Japan.