Thermal reaction in growth of rice plants at the vegetative growth stage. Comparison among different ecotypical groups.

Abstract

Thermal reaction in the growth of rice plants at the vegetative stage was compared among different ecotypical groups. Eighteen varieties including 4 japonica, 2 javanica, 5 indica, 4 Chinese-indica and 3 Tongil group (an indica-japonica-cross variety group bred in Korea) were used (Table 1). Treatment temperature was set at a day-night regime (0600-1800 hours) of 20∼10°C, 25∼15°C, 30∼20°C or 35∼25°C in a natural light room of the phytotron. The treatments for 20 days started at the 4-, 6- or 8-leaf stage in Experiment I, at the 4- or 6-leaf stage in Experiment II, and at the 4- leal stage in Experiment III. The increments in plant height, stem number, leaf age and leaf dry weight were followed in the course of the temperature treatments (Figs. 1∼8). As for plant height, japonica and javanica varieties showed higher elongation activities (comparative values with the 30∼20°C plot) than the varieties of other types under the cool temperature conditions, and indica and Tongil group varieties were higher in elongation activity under the high temperature condition (Fig. 9, Tables 2 and 3). The data on stem number showed inconsistencies among repeat experiments and also among different varieties in the same type, and thus no clear tendencies were found (Fig. 10, Tables 2 and 3). Leaf age did not show much difference among different ecotypical groups. The comparative increments tended to be larger in Tongil group, Chinese-indica and indica varieties at the cool temperatures, while at the high temperature in japonica, Tongil group and Chinese-indica varieties (Fig. 11, Tables 2 and 3). As for leaf dry weight, japonica and javanica varieties showed larger comparative increments at the cool temperature regimes, and Tongil group did the largest at the high temperature regime (Fig. 12, Tables 2 and 3). Table 4 summarizes the above-mentioned results. Generally speaking, japonica varieties showed the highest adaptability to the cool temperatures, Javanica type was close to japonica, and the other 3 types were clearly lower in adaptability. At the high temperature, Tongil, indica and Chinese-indica types showed higher adaptabilities than japonica and javanica types though the difference was comparatively small. This paper confirmed general ideas, which have been induced from many data in papers on related subjects, on the difference in the thermal reactions among different ecotypical groups of rice plants. Further elaborate studies on this line is expected, particularly studies based on physiological analysis of metabolism using a larger number of varieties in each ecotypical group.