Abstract:Among 136 somaclones, five mutants of thermo-sensitive gen ic male sterile rice were obtained by somatic cell culture from two male sterile (MS) lines, IR66707A and IR69700A, which are of cytoplasmic type. The mutants w ere sterile during late spring until early autumn, and became fertile in late au tumn (the end of October) in Guangzhou. In midsummer, when the mutants of young panicle developmental stage to pollen formation stage were used for short-day tr eatment (daylength was adjusted to 8 h daily for 30 days)，all the mutants were still sterile whereas the Nongken 58S (contro1) was converted to be fertile．However,when the mutants were treated under low temperature(22±1℃)for 10 or more days,they became fertile，the seed setting percentage being 17.23％-42.1 9％， whereas those under normal condition (high temperature) were still sterile．These results showed that the fertility conversion in mutants was correlated with temperature rather than with day length． If the mutants were used as female parent to cross with normal variety,the plants in F1 were all fertile，while in F2 were segregated into 3(fertile):1(sterile)，and in testcross F1 were in the ratio of 1：1． Genetical analysis indicated that the mutants were controlled by a pair recessive genes．In this experiment，we obtained a thermo-sensitive genic MS mutant that derived from cytoplasmic MS.