抄録
1. Experiments were conducted as a part of the series of fundamental researches on the relationship between day-length and the action of genes E1 and E2 controlling heading date with the aim of obtaining some information on rice breeding. 2. Strains which possess E1 and E2 m different, combinations homozygously (Table 1) were maintained under various photoperiodical treatments (Fig. 1), and the variation in heading date and ear primodium differentiation were observed. 3. The findings are as follows : The genes E1 and E2 have little effect on the period necessary for acquiring short-day sensitivity (35-40 days after sowmg m all the stralns) (Fig. 2 and Table 2). The effect of genes E1 and E2 on heading date is closely related to the length of photoperiods(Fig. 3). Under the common environment of rice culture where the photoperiod decreases gradually, the time of ear primordium [differentiation is determined mainly by the genotypically specific "criticalday-length" (Fig. 4). The effect of gene Ei on the critical-day-length is larger than that of gene E2. The critical-day-length seems to become longer as the plant becomes older (Fig.5). 4. These findings may be important in understanding the relation between genetic and environmental effects on character development.
