Effects of air temperature and light on grain filling of an indica and a japonica rice (Oryza sativaL.) under controlled environmental conditions

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Abstract
The effects of air temperature and light on the grain filling of an indica (IR20) and ajaponica rice (Fujisaka 5) was studied in artificially lighted cabinets. Within the daily mean temperature range of 16° to 28°C, the higher the temperature, the faster the grains filled and matured. At 28°C, the upper grains of IR20 rice took 13 days to reach the maximum weight, whereas those of Fujisaka 5 took 18 days. The optimum daily mean temperature range to achieve maximum weight per grain was 19° to 25°C for IR20 and 16° to 22°C for Fujisaka 5. Apparently, IR20 rice is better adapted to higher temperatures during the ripening period than is Fujisaka 5 rice. More chalky grains occurred when the temperature was above or below the optimum range. Both day and night temperatures affected grain weight and grain quality. The daily mean temperature was found to be the most meaningful expression for describing the effect of temperature on grain filling. Low light intensity appeared to cause a slight delay in the grain filling of the whole panicle and a reduction in the percentage of filled grains on the lower branches. A combination of high light intensity and low temperature gave the best ripening grade (grain weight × percent filled grains).

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