Genome analysis and genetic mapping of restorer loci in raphanus
Genetic variation exists in Raphanus that could be of use to Brassica breeders. Of particular interest is the Ogura system of cytoplasmic male sterility (CMS) which has been worked on extensively in a Brassica napus background. Problems have been experienced in B. napusrestorer lines due to the inheritance of a large segment of Raphanus chromosome containing the fertility restoring locus. This restorer introgression is located on the Brassica C genome making it only of use for B. napus and not for B. rapa or B. juncea. This thesis describes the development of the materials necessary for the introgression into the Brassica A genome of a defined segment of Raphanus chromosome containing a restorer locus. Defined genetic stocks of Raphanus were developed that contained specific loci controlling restoration of Ogura CMS. This material was used to develop populations segregating for specific restorer loci. Extensive RFLP maps of three Raphanus populations were developed and aligned, resulting in a robust consensus map of the entire Raphanus genome. Three restorer loci were accurately mapped on three separate linkage groups. The segment of Raphanus that is implicated in the restoration of Ogura CMS in a B. napus restorer line developed by INRA was identified and it did not correspond to any of the regions containing the three mapped restorer loci, suggesting the presence of more restorer loci in Raphanus. Comparative mapping between the Raphanus genome map and previously generated Brassica A genome RFLP maps demonstrated large regions of collinearity between segments of chromosomes of the two species. Preliminary examination of the two genome maps suggest they contain essentially the same overall genetic content but with large segments of the genomes rearranged with respect to each other. Likely sites of Raphanus restorer introgression into the Brassica A genome were predicted. Trigenomic tetraploids were developed in which pairing and recombination between homoeologous segments of Raphanus and Brassica A chromosomes should result. Progeny of these individuals will allow an assessment of the pattern and extent of recombination that occurs between the chromosomes of the Raphanus and Brassica A genomes and should lead to the development of 'B. napus' lines carrying Ogura CMS restorer alleles from Raphanus.
Brassica A genome, plant science, gene mapping, cytogenetics, radish - genetics, cytoplasmic male sterility, Ogura CMS, Raphanus genome
Doctor of Philosophy (Ph.D.)