| Polima (pol) CMS has been widely used for hybrid breeding, but how to select its appropriate restorer lines has been a major factor in the process. The molecular markers linked to the fertility restorer gene (Rfp) will speed the breeding of elite restorer lines.The spread of hybrid rapeseed has an important role of increasing the product of rapeseed, however, the present hybrid rapeseed cultivars were easily susceptible to Sclerotinia sclerotiorum (Ss) on different degree. It is an efficient way to improving the resistance of hybrid rapeseed by introgressing the resistant genes from the resistance materials to the restorer lines. In general, it is difficult to generate resistance varieties by conventional backcross. Molecular markers can be use'd as a selecting tool for backcross breeding because the molecular marker-assisted selection (MAS) can not only precisely select the targeted gene but also quickly delete linked drags.The objectives of this study aye mapping the Rfp and developing Ss-resistance restorer lines by MAS. The main results are as follows:1. In order to map Rfp, a backcross population, [(1141A Hui5200) 1141B] BC1F1, was constructed. There were 72 fertile and 66 sterile plants in the population. The segregation ratio of fertility: sterility agreed with expectation 1:1. It showed the fertility of pol CMS was controlled by a pair of dominant genes.2. Bulked segregant analysis was adapted to identify RAPD markers linked to the Rfp of pol CMS. DNA bands amplified from 1040 random 10-mer primers were screened. Two polymorphic bands S1019. 720 and S1036. 810 were found linked to the Rfp locus at the same side with a map distance of 5. 8cM and 12. 3cM, respectively.3. These polymorphic fragments were cloned and sequenced. Nucleotide sequence information was used to design 20-24-mer oligonucleotide primers for PCR amplification. The SCAR markers (SCS1019.720 and SCS1036.745) generated from the primers showed the same pattern of segregation as the original RAPD markers in the backcross population.4. By screening 92 Arabidopsis thaliana ESTs clones and 120 rapeseed genomic probes, 3 RFLP markers were found linked to the Rfp locus. 2 flankingmarkers were wg3h8. 7000 and ec3b4. 3200, and the nearer one was 18. OcM from Rfp. According to the linkage group of these probes located, Rfp was located at the distal end on the 5th linkage group of Ferreira map (1994).5. In order to analyze the genetic characteristic of resistance to Ss, one backcross population, [(Hui5200 NingRS-1) x Hui5200] BC1F1, was constructed. The frequency distribution of lesion diameter was a normal one in the detached-leaf inoculation of seedling stage. It showed that multiple genes in rapeseed controlled the resistance to Ss.6. 27 resistant plants were selected from 279 individuals of BC1F1 population by field inoculation and 2 SCAR markers linked to Ss. According to the genetic background analysis of 61 RFLP markers and 88 RAPD markers, 1 plant, which was the most similar to the Hui5200 genotypes, was selected and used for next backcrossing.7. Using the same method, 30 seedling resistant plants were selected from 393 plants of BC2F1. By genetic background analysis with 63 AFLP and RAPD markers, 10 plants of similar to the Hui5200 genotypes were selected, selfed and used as pollinators to testcross with 1141A. Among them 3 plants were selected by the resistance to Ss in adult stage and the result of background analysis with another 63 PCR markers. So the seeds of the 3 selfed and testcross were sowed.8. 2 candidate plants (RSH1 and RSH2) with Ss-resistance were selected from the self-fertilizing offspring whose ancestor plant had homozygous genotype of RfpRfp. The self-fertilizing offspring of these 2 plants are the Ss resistance restorer lines.9. Compared the selective efficiency of RAPD, RFLP and AFLP markers in genetic background selection, AFLP marker was found to be the ideal one. At last, some questions coming out in genetic background selection were discussed.
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