Effects of Air-Temperature and Water-Temperature at Each Stage of the Growth of Lowland Rice : II. Effect of air-temperature and water-temperature on the heading date

摘要

Growing the rice plants under various conditions of some possible combinations of daytime air-temperatures (AD : 26, 20 and 14°C), the daytime water-temperatures (WD : 26, 20 and 14°C), the nocturnal air-temperatures (AN : 20, 14 and 8°C), the nocturnal water-temperatures (WN : 20, 14 and 8°C) and the number of days of treatment (P : 3, 6 and 9 days), the authors examined their main effects and interactions on the heading date. The rice variety "Eiko" was used. The daytime was settled for eight hours from 9.00 a.m. to 5.00 p.m. and the night-time was settled for sixteen hours from 5.00 p.m. to 9.00 a.m. of the next day. The water was kept four cm. in depth above the soil surface in pots. The experimental design was 35 factorial in 81 units (1/3 replicate) with one block and defining contrasts 1=ADWDANWNSUP2P. The results were summarized as follows; 1. At the fourth leaf stage (T1; the transplanting time), the main effects of WD, WN and P were significant at 0.1% level and all the other were not significant (table 2). And regardless of the difference of WN, it was inferred that WD of 21°C hastened the heading date (fig. 1-T1(P3)). 2. At the seventh leaf stage (T2; about ten days before the differentiating stage of first bract primordia), the main effects of AD, WD, AN and WN and the two-factor interactions of AD × P, AN × WN and AN × P were significant. The contour lines of each date of heading based on WD and WN were almost straight and parallel with the line of mean water-temperature for nine days treatment (fig. 1-T2 (P3)). On the other hand, the contour lines of each date of heading based on AD and AN were curved. And regardless of the difference of AN, it was inferred that AD of 20°C hastened the heading date (fig. 2-T2 (P3)). Moreover, T2 was considered to be the most sensitive stage to temperature, because the heading date and the total leaf number on the main stem were most variable by both air- and water-temperature among all the treatment stages. 3. At the stages of nine leaves (T3; the differentiating stage of first bract primordia) and ten leaves (T4; the middle differentiating stage of primary branch primordia), the main effects of each factor and their interactions were similar to those of T2, but the strengths were weaker than those of T2 (table 2, 3 and 4). 4. At the thirteenth leaf (flgg leaf) stage (T5; the stage of reduction division of pollen mother cells), the main effects of AD, AN and P and the two-factor interaction of AN × P were significant greatly (table 2). The contour lines of each date of heading based on AD and AN were almost straight and parallel with the line of mean air-temperature (fig. 2-T5 (P3)).