Genetic Analysis Of Fertility Revertants In CMS Lines Of Rice (Oryza Sativa L.)

Cytoplasmic male sterility (CMS) system is an important basis for development of hybrid rice, in which hybrid seed purity and the heterosis are affected directly by CMS line purity. Existence of the fertile plants (FPs), which are similar to CMS plants in phenotypes except fertility, is a common and serious problem in production of hybrid seeds. Researches on genetics and source of the FPs would benefit to production of high purity hybrid seeds, as well as benift to understanding origin and variation of rice CMS and fertility restoring genes.The populations of CMS-D1 (Dian type 1) lines, LiyuA, Yumi15A and Hexi42A, were generated through CMS multiplication with bagging method, which is very effective to prevent CMS lines pollinated by other varieties. Of 0.0573% FPs on average was found in the CMS populations. Analysis based on crossing, backcrossing, and DNA markers showed that two types of the fertile plants were existed in the CMS population.One type was acount about 72.97% in the total fertile plants. They produced more than 97% fertile pollens, and could self-pollinated with normal seed-set, but they did not carry fertility restoring (Rf) gene. They had N(rf/rf) genotype, the same as that of CMS maintainers. They would be derived from contamination of maintainers in production of CMS seeds. They could be reduced, even eradicated by restriction procedure in CMS seed production.Another type FPs was these that still kept CMS cytoplasm, the same male sterile cytoplasm as that of CMS-D1 lines. They produced about 50% fertility pollens, and had heterozygous genotype Rf/rf, designed as Rfr(d1), which could make CMS-D1 lines fertility restored in gametophytic mode. Frequency of these plants was 0.0155% in CMS populations. They should be generated though from fertility reversion of CMS, and were designated as fertility revertants. Allelic test showed that Rfr(d1) was allelic to that of CMS-D1 restorers, and the gene was located within rice Rf-1 locus, which was identified by two CAPS markers located within rice Rf-1 locus. Progenies of these fertility revertants did not show segregations at morphologic traits, and did not show polymorphism against with their original CMS lines when 169 microsatellite loci were analyzed. Therefore, Rfr(d1) could not be generated by contamination of Rf gene from alient varieties,but be generated spontaneously through reversion of rf genotype in CMS lines. It is the first report of verifying existence of the fertility revertants in rice CMS populations by genetic and DNA marker techniques.