Genetic analysis of male sterility in rice mutants with environmentally influenced levels of fertility

Twenty-six male sterile plants grown in the field were recovered in the M7 generation from ethyl methane sulfonate-treated material of the rice cultivar M-201. Fertility increased five-fold when ratooned plants from the field were grown in a growth chamber with a 12 hour daylength. Crosses between mutant and normal fertile cultivars produced fertile F sub(1) plants. Female fertility was normal as judged by percent seed set from unbagged panicles of parental and recombinant lines. Transgressive segregation for fertility was observed for all crosses in the F sub(2) and F sub(3) generations. Five of 37 F sub(3) male sterile plants showed moderate levels of seed fertility under winter greenhouse conditions and reduced seed set when transplanted to summer field plots. Fertility data from reciprocal crosses suggested cytoplasmic factors had little or no effect on levels of male sterility in the mutant lines. Chi-squared analyses of F sub(2) and F sub(3) generation results indicated male sterility of the mutants is conditioned by two nuclear genes with epistatic effects.(DBO)