79 cases of male sterile variants in seven rice materials, Zhenshan 97B, Hongyuan A, Baoyuan A, W6154s, IR26, Minghui 63 and Nanguang-zhan were found, in which 72 cases belonged to R1 generation (regenerated plants from rice somaclones), and seven to R2 generation (plants from first self-pollination, viz, progeny obtained by self-fertilizing the regenerated plants). 10 673 regenerated plants were obtained in R1 generation, the frequency of male sterile variation was 1.02% (0.85~1.08%). Male sterile variants were found in Zhenshan 97B and Taiyin 1 in R2 generation, and the average male sterile variation frequency in Zhenshan 97B and Taiyin 1 was 2.22% and 1.89% respectively. Abortive pollen of rice could be classified into four types: pollen free type (PFT), typical abortion type (TAT), spherical abortion type (SpAT) and stained abortion type (StAT). The phenomenon that type of pollen abortion could change from one to another through tissue culture was found in rice somaclones in R1 generation. One chimera was obtained from R1 regenerated plants of IR26 and Minghui 63 respectively. Fertility segregation was found from R2 generation of Taiyin 1 and Zhenshan 97B respectively. Genotype was the main reason in the course of inducing male sterile variants. Male sterile variation was found in all rice materials except Nongken 58s, IR24, Zhenshan 97A and Taiyin 1 in R1 generation. Dedifferentiation of explants was essential to producing male sterile variation, and 2,4-D played a decisive role in this course. The frequency of male sterile variation in somaclones might be affected by the duration of subculture passage. The frequency of male sterile variation in R2 generation (around 2%) was higher than that in R1 generation (around 1%). The higher frequency of male sterile variation in R2 generation showed that the mutant frequency of one site of a pair of genes from the wild type was much higher than that in a homozygous mutant (two sites of a pair of genes undertaking mutants at the same time).

Key words: cytoplasmic male sterility (CMS), fertile reversion, in vitro culture, indica, japonica, Oryza sativa L.