ABSTRACT

Information on the genetics of fertility restoration in a cytoplasmic male sterility (CMS) system is helpful in the selection of restorer lines used in hybrid breeding programs. In the present investigation genetics of fertility restoration for Wild Abortive (WA) type CMS in rice (Oryza sativa L.) was studied utilizing two CMS lines (IR58025A and IR62829A), their respective maintainers (B lines) and two restorer lines (KMR3 and IR10198R). Two F2 populations and five back cross populations were analyzed for their spikelet fertility percentage to calculate the genetic segregation ratio. The fertility restoration of F2 populations fitted to a 15:1 (fertile: sterile) segregation ratio and that of back cross population fitted to a 3:1 (fertile: sterile) ratio. This indicated that two independent dominant genes with duplicate gene interaction controlled fertility restoration in all the populations.

To validate the reported molecular markers, eight RAPD markers, nine SSR markers and three CAPS markers reportedly linked with the fertility restorer genes of different sources of cytoplasm were analyzed following bulked segregant analysis. Two unreported SSR markers RM311 and RM474 were also analyzed. Two mapping populations, one F2 population from the cross IR58025A/KMR3 consisting of 347 individual plants and one back cross population from the cross IR62829A// F1(IR62829A/ IR10198R) with 130 individual plants were used in this study.

Of the eight RAPD markers analyzed, none gave polymorphism between the parents and their extreme bulks in both the populations studied. One of the primers OPK05 did not show any amplification.

Of the eleven SSR markers analyzed (9 reported and 2 unreported), eight primer pairs, RM6100, RM228, RM171, RM216, RM474, RM311, MRG4456 and pRf 1 & 2, gave polymorphism between IR58025A and KMR3. Two primer pairs, RM6100 and RM474 gave polymorphism between parents of back cross population (IR62829A and IR10198R). The positive markers were tested on 347 F2 plants and 130 back cross plants. Based on the banding pattern of A lines, R lines and F1, the scoring was carried out.

One out of three CAPS primers gave polymorphism between IR58025A and KMR3 after digestion with the reported restriction enzymes. This primer pair was then used to survey the F2 mapping population. None of the CAPS primers developed polymorphism between the parents and their extreme bulks of the back cross population.

The selection accuracy of RM6100 was checked using 21 restorer lines and 18 maintainer lines. Except two R lines, IR66 and C-20 R, all the other R lines showed distinct polymorphism between R and B lines. It showed a selection accuracy of 94.87%. The results indicated that the microsatellite marker RM6100 would facilitate marker-aided selection (MAS) for restorer lines in the CMS-WA system, which will be very helpful in identifying the restorer lines from large number of genotypes most expeditiously with good accuracy. This will enhance the efficiency of hybrid rice breeding program.

Segregation of DNA markers for the Mendelian inheritance was analyzed using chi-square test. Except RM216 all other markers fitted to co-dominant segregation ratio 1:2:1. The co-segregation of these markers with the Rf trait was analyzed using ‘t’ test and the result revealed that the markers RM6100, RM228, RM171, pRf 1 & 2 and RG140FL/RL were associated with the Rf trait.

A local linkage map based on the scores/genotypes of marker loci was constructed using Mapmaker analysis. The linkage analysis revealed that the Rf trait is linked to RM6100, RM171, pRf 1 & 2, RM228. RM6100 was the one marker that is more closely linked to this locus. The genetic distance between RM6100 and pRf 1&2 / RM171 was calculated 1.9cM and those between pRf 1&2 / RM171 and RM228 was calculated 22.1 cM.

QTL mapping of Rf trait revealed that the highest phenotypic variance is located between markers RM311 to RM6100. The position of QTL is located near to RM6100. The results also explained that RM6100-RM228 is the region containing the QTL controlling the Rf trait.