Studies on the relationship between genetic and environmental effects on character development. : 2. Response of the genes E₃, E₄ and E₅ to day-length in rice.

Abstract

1. Following the previous report (KAWASE and MURATA 1958), five experiments were conducted as a part of the series of fundamental researches on the relationship between day-length and the action of genes E₃, E₄ and E₅ controlling heading date with the aim of obtaining some information on rice breeding. 2. Seven strains which possess E₃, E₄ and E5 in different combinations homozygously (Table 1. ) were maintained under various photoperiodical treatments and the variation in heading date and ear primordium differentiation were observed. 3. The findings concerning the function of genes E₃, E₄ and E₅ for the response to day-length treatments are nearly the same as those obtained with the genes E₁ and E₂ (KAWASE and MURATA 1958) and summarized as follows : The period necessary for acquiring short-day sensitivity are nealy the same for all strains (35-40 days after sowing), and thus the genes E₃, E₄ and E₅ have little cefect on this period. In the sensitivity to the 12-13 day-length treatment after acquiring short day sensitivlty, there were no differences among the seven strains. But genotypic differences come out distinctly under the 14-16 day-length treatment. The effect of gene E₄ on the response to day-length treatment is larger than those of gene E₃ and E₅. This relationship between the effects is unchangeable in all four plant ages examined. 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 "critical-day-length". The effect of gene E₄ on the shortening of the critical-day-length is larger than those of genes E₃ and E₅. The heading clate is ddlayed when the dominant alles of E₃, E₄ zind E₅ are included and the day-length is longer. It is physiologically due to the increase in the nulnbers of days from photoperiod treatment to differentiation of ear primordium and from this time to heading. Furthermore, the effect of short-day treatment on ear emergcnce is lesser in the young plant than the old. From these findings and the fact that the genes E₃, E₄ and E₅ giv'e some influence on plant height, it was supposed that these genes are controlling the synthesis or metabolism of auxins in plant in some way.