Abstract
Two kinds of modifiers for SD system on the second chromosomes, Ac(SD)-like and St(SD)-like were examined on a natural population, Odate, Japan. Among 21 isofemale lines six lines carried Ac(SD)-like and five beared St(SD)-like modifiers. None of the second chromosomes examined beared both of these two kinds of modifiers simultaneously.
The effects of these modifiers as a suppressor or a enhancer of SD were not so stable and were differently affected by different Recombinant-SD, i.e., RSD1and RSD2. In general, the k values of RSD1/Ac(SD)-like or RSD1/St(SD)-like males were higher than those of RSD2/Ac(SD)-like or RSD2/St(SD)-like males respectively. These results probably came from the different strength of distortion in these two SD strains.
From the results of mapping experiments, Ac(SD)-like was located near cn locus, and it was estimated to be Ac(SD) itself. The results of fecundity experiments also supported this conclusion.
A St(SD)-like modifier which was located on an inversion free second chromosome seemed to consist of at least two elements. Therefore this St(SD)-like was concluded not to be St(SD). On the other St(SD)-like associated with NS inversion, any direct genetic analysis was impossible.
