Young panicles from 11 rice varieties, Zhenshan 97A (WA type cytoplasmic male-sterile (CMS) line, indica), Zhenshan 97B (WA type maintainer line, indica), IR24, IR26, Taiyin 1 and Minghui 63 (WA type restorer line, indica), Hongyuan A (HL type CMS line, indica), Baoyuan A (BT type CMS line, indica), Nanguangzhan (genic male-sterile (GMS) line, indica), Nongken 58s (photoperiod-sensitive genic male-sterile rice (PGMR), japonica) and W6154s (thermosensitive genic male-sterile rice (TGMR), indica), were cultured on different media. Regenerated plants were obtained. Pollen fertility was examined. Factors influencing the in vitro screening of male-sterile variants were discussed. The main results were as follows: During the eight years of 1991~1998, 78 cases of male-sterile mutants (or variants) in seven varieties (Zhenshan 97A, Zhenshan 97B, IR26, Hongyuan A, Baoyuan A, W6154s and Nanguangzhan) were found, in which 74 cases belonged to R1 generation and four to R2 generation. Genotype was the main reason in the course of inducing male-sterile variants. Male-sterile variation was found in all rice varieties 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 mutant at the same time). Based on the result of this experiment, the authors suggested that some chemicals in the medium might cause the mutant during culture in vitro.

Key words: cytoplasmic male sterility (CMS), genic male sterility (GMS), in vitro screening, indica, japonica, Oryza sativa L.