Tohoku Journal of Crop Science

By using two varieties, Norin No. 1 (many panicle type) and Zosan No. 1 (heavy panicle type) an experiment was made in the growth cabinet to examine the influence of light and dark temperature range on the emergence and growth of tillers. Light temperatures adopted were 15°, 20°, 25°, 30°, 35°, and 40°C, and dark temperatures 15°, 20°, 25°, and 30°C ; 23 combinations were made of these temperatures excepting the combination of 40°C in the light period with 30°C in the dark. Light and dark temperature ranges plotted were 0°, 5°, 15°, 20° and 25°C. The daylength was controlled so that the light period could be 16 hours and the dark 8 hours. Observations of the emergence of tillers were carried out in response to the leaf age of the main stems. The results were : 1) In the case of Norin No. 1,tillers emerged and elongated on Katayama's theory of tillering in the temperature range from 20°C to 40°C under conditions of the above-mentioned respective temperature ranges. 2) The temperature range suitable for tiller emergence and elongation was narrower in Zosan No. 1 than in Norin No. 1 and the number of tiller decreased especially in the high temperature range. High temperature was the controlling factor in tiller emergence.

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The purpose of this experiment was to investigate the effects of temperature during the vegetative growth stage and the reproductive stage on the growth and yield of rice plant under the condition of controlled environment. Results obtained are summarized as follows : 1) It was reaffirmed that the factor affecting the ripening or rice plant was not only the environmental conditions during the ripening stage but the environmental conditions during the vegetative growth period also played an important role in the ripening of the grains. 2) It seemed that the ripening was controled mainly by the temperature during the reproductive period in the cultivars adapted to the cold districts, and the temperature during the vegetative growth period, however was more important in the cultivars adapted to the warm districts for the ripening of the grains. 3) Influences of the temperature during the vegetative growth period on grain ripening and yield was very slight due to the shorter period of the vegetative growth stage. The significant effect of temperature during the vegetative growth stage, on the other hand, was found in the cultivars adapted to the warm districts of Japan. which had the lower thermosensitivity and the longer vegetative growth period.

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The effect of light intensity on the photodestraction of chlorophyll under low temperature was studied in rice plants, Norin No. 20,Dular and Chinsurah Boro II. 1. Decrease of chlorophyll contents in Norin No. 20 was recognized only by the removing from weak to strong light intensity under the low temperature (15°C) condition. The fact suggests that the photodestraction of chlorophyll is remarkably caused by the strong light intensity. 2. When the rice plants were changed from high (25°C) to low (15°C) temperature, the decrease of chlorophyll contents was observed in all cultivars used, especially under strong light intensity. The result shows that strong light intensity may induce the severe photodestraction of chlorophyll under the low temperature.

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The effects of the pre-treatment of low temperature on the expression of chlorosis were examined during the leaf growth process in rice plants. 1. When the base of shoot was pre-treated by low temperature, the second leaf emerged after the pre-treatment showed chlorosis, although the other plant parts were exposed under high temperature. The expression of chlorosis may be caused by the low temperature sensitivity of leaf primordium (ca.1mm) enclosed in the shoot base. 2. The transferring from high to low temperature (15°C) induced the chlorosis in the second leaf emerged after treatment, while the change from low to high temperature (25°C) formed normally the chlorophyll in the third leaf emerged after the treatment.

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