Effect of Air Temperature on Floral Induction by Short Day in Rice Plants

Abstract

Experiments were conducted to make clear the differences of floral induction in rice plants as affected by air temperature during short day treatment, using a daylength-sensitive variety Zuiho. The plants of 12∼14 leaf stages were subjected to 10-hour photoperiod under various air temperatures in growth cabinets with natural light. The results obtained are summarized as follows. 1. The plants were subjected to 10-hour photoperiod under various constant temperatures; 12°, 16°, 20°, 25°, 30°, 35° and 40°C. The short day effect was largest at 30°C, and decreased with rising or falling of temperature from the optimum, 30°C(Fig. 1). Short day treatments gave no effect at 12°C or 40°C. The optimum temperature for the short day induction was somewhat lower than that for leaf emergence (Fig. 2). 2. The plants were subjected to 10-hour photoperiod under lightperiod temperature from 16°C to 40°C and darkperiod temperature from 12°C to 35°C (Table 1). Both the optimum temperature for lighperiod and darkperiod were 30°C although 25°C during the darkperiod gave the same effect as 30°C (Table 1, Table 2, Fig. 3). Short day effect decreased when the temperature was lower or higher than the optimum one. Differences in short day effect due to lightperiod temperatures were almost the same as those due to darkperiod temperatures with the exception of temperatures higher than 30°C (Table 3). When the range of temperature between the light- and darkperiod was 5°C, the effect of short day was almost the same as that under constant temperature throughout the both periods (Fig. 4). A smaller effect was obtained when the range was larger than 10°C.