1960 Volume 29 Issue 1 Pages 75-78
The experiments were carried out to know the bad effects due to high water temperature upon the young panicle development of the rice plant in reference to root growth. I. Pots with rice plants were immersed in the water tank which were regulated to three constant temperatures, namely, 26°C, 32°C and 37°C during the period of the young panicle development. One set was placed in the open air and the other in the greenhouse. (a) In the outdoors, by the 32°C threatment, the number of developed spiklets per panicle were decreased but the number of differenciated spiklets were not affected and both numbers were decreased by 37°C treatment, comparing 26°C. These injuries were promoted in the greenhouse, especially in the plants with 37°C treatment heading was not observeb. (b) At both 32°C and 37°C treatment, the amount of roots reached the peak at the middle stage of young panicle development, and thereafter decreased once, and again increased until heading date at 26°C. The number of rotten root of the plant remarkably increased at high water temperature plots, especially in 37°C plots during the later half period of young panicle development. II. In the paddy field, the effects of lowering water temperature by continuous watering during the period of of young panicle development were investigated. The temperature condition in each plot is shown in Fig. 5. The total number of developed spiklets per hill showed the greatest value in the plots which subjected to ca. 26°C in mean temperature and less than 32°C in maximum temperature. From the results of experiments, the following consideration may be made. Optimal water temperature to the young panicle development of rice plant lies at 25-30°C. Higher water temperature than ca. 32°C increases the number of root rot of the plant and consequently couses the damage of the development of spiklets.
