Fertility behaviour of rice ( Oryza sativa) lines with dominant male sterile gene and inheritance of sterility and fertility restoration

Abstract

The genetic basis of male sterility and fertility restoration of the Pingxiang male-sterile rice (PMSR) was studied using progeny populations created between PMSR and 11 fertile lines. It was found that the male sterility was determined by two interacting (epistatic) dominant nuclear genes, one for sterility and one for fertility restoration. The dominant sterile gene expresses as male-sterility when existing solely, but as normally fertile when coexisting with the restoration gene. The individuals with only the restoration gene are normal and fertile. A homozygous sterile line developed using PMSR by repeated selfing was characterised for its fertility behaviour under controlled and field conditions. Male fertility was affected by both temperature and photoperiod with temperature being more important. The critical temperature for inducing fertility was 27–28 °C. Blow this critical temperature, plants remained sterile, but become partially fertile at higher temperature. The panicle development stages that are sensitive to temperature were from differentiation of the secondary branch primordium (S3) to the meiotic division of the pollen mother cells (S6). Continuous high temperature (>30 °C) during these sensitive stages is necessary to maintain male fertility. Long photoperiod (15 h) induced partial fertility even under temperature, which could induce sterility. In practice, this line can be regarded as thermo-sensitive. In the sub-tropical zone, this line has complete sterile phase longer than 4 weeks and thus is suitable for hybrid production using the two-line system (a pair of pure sterile and fertile lines). Male sterile line required low temperature and short photoperiod to express male sterility, like the one derived from PMSR, has never been reported in any crop species. This line is also the first dominant nuclear male-sterile line that could be exploited for hybrid seed production using the two-line system.