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One of the potential risks in two-line hybrid system is caused by unpredicted low temperature below the critical level in hybrid seed production season under natural condition that leads to self seed setting in female parent. To overcome this, rice breeders are working for breeding photoperiod-sensitive genic male sterile(PGMS) and Thermo-sensitive genic male sterile(TGMS) lines with a lower sterility-inducing critical temperature, as well as focusing on the exploration of reverse PGMS and/or TGMS that are sterile under short day-length and/or low temperature, but fertile under long day-length and/or high temperature. These can be used as female parents during the short day-length and /or low temperatures while the normal PGMS or TGMS are used as female parents under long day-length and/or high temperature. So in this study, the analysis of pollen fertility of D52S and D38S strains responses to photoperiod during the sensitive stage under natural and controlled conditions, the inheritance and molecular mapping were performed to ascertain whether the D52S and D38S are reverse PGMS lines, to identify the inheritance model and DNA markers that co-segregate with gene conferring short/reverse photoperiod-sensitive genic male sterility(rPGMS) in D52S mutant rice.
Results indicated that D52S and D38S plants were fertile when headed from mid August to mid September; they were however, sterile when headed after Sept 30 whereas N5088S, a normal PGMS line showed the opposite results. The fertility alteration condition was day-light〉13.75 h below which D52S and D38S were sterile. The pollen fertility distributions of F2 populations from D52S/Shuhui and D52S/G99 crosses, showed a 3:1 ratio of fertile to sterile plants. The male sterility in D52S germplasm was therefore considered to be controlled by major recessive nuclear gene. Chi square(x2) test for single gene segregation(p〈0.5) confirmed that short PGMS phenotype segregated as a single gene. Polymorphism between the two parents, D52S and Shuhui527 was 33％. This genetic diversity indicated a higher heterosis thus D52S rice is a good line that can be used in two-line system rice breeding programs as a female parent while Shuhui527 serves as male parent. Eight markers, RM474 RM33OA, RM2571, RM244, RM2887, RM216, RM8207 and RM3311 located on chromosome number 10 cosegregated completely with the rpms locus. The locus was named rpms3(t) gene and was mapped to the interval between SSR markers RM2571 and RM244 at a distance of 6.6 cM and 4.6 cM, respectively.
Lu et al(2008) reported that rPGMS in YiD1S was controlled by two recessive genes, rpms1 and rpms2 located on chromosomes 8 and 9 respectively. Previous studies have indicated male sterility in two-line systems obey single-locus, two-locus or diverse genetic models(Virmani 2003a). Another research or allelism test is important to support one or both of these findings.
KEYWORDS: Male-sterility, reverse PGMS, D52S line, inheritance study, DNA markers, Gene mapping