Genetic Analysis of Fertility Revertants Identified in Rice CMS Populations

Abstract

The contamination of cytoplasmic male sterile (CMS) populations by fertile plants (FPs), which reduces purity of hybrid seeds, is a common problem in hybrid seed production, but genetic characterization of FPs has not been undertaken in rice (Oryza sativa L.). In this study, two types of FPs were identified among 64,530 plants of three CMS lines of Dian type 1 (CMS‐D1), in which the CMS seeds were produced under strict isolation. One type of FP had a genetic background identical to that of the CMS maintainers, which was revealed by 169 simple sequence repeat (SSR) markers and nine morphological traits. This type of FP was found at a frequency of 0.0418% in the CMS populations. These FPs could have resulted from maintainer contamination. Another type was a fertility revertant (FR), occurring at a frequency of 0.0155% in the CMS population. Although the FRs did not show differences from the corresponding CMS lines in morphological traits and the SSR markers, they possessed a fertility restoring gene of heterozygous type, which acted in gametophytic mode on pollen fertility restoration of the hybrids. The gene was designated temporarily as Rfr(d1). Rfr(d1) was allelic to the fertility restoring gene carried by CMS‐D1 restorers, and it was located at the Rf‐1 locus, which was revealed by allelic testing and cleaved amplified polymorphism sequence markers located within the Rf‐1 locus. Fertility revertants could be generated spontaneously through reversion of CMS lines.