Genetic relationships within the Brassica oleracea cytodeme: comparison of molecular marker systems
1997
Lanner, C. (SLU, Svaloev (Sweden). Inst. foer Vaextfoeraedling)
Genetic relationships of wild Brassica species related to B. oleracea are discussed in the thesis. A review of methods used to determine genetic relatedness and examples of their application to the genus Brassica are given. Four studies of the relationships of the B. oleracea cytodeme, using either different molecular marker systems or at different levels of organismal organization, are discussed relative to comparable investigations. The Brassica oleraceae cytodeme encompasses a group of interfertile Brassica species with the chromosome number 2n=18. Wild species are endemic to the Mediterranean region and the Atlantic coastal regions of Spain, France, and Great Britain. The species comprising the cytodeme are B. bourgeaui (Webb) O. Kuntze, B. cretica Lam., B. hilarionis Post, B. incana Ten., B. insularis Moris, B. macrocarpa Guss., B. montana Pourret, B. oleracea L., B. rupestris Rafin., and B. villosa Biv. Horticultural forms of B. oleracea are interfertile with the wild species and are therefore part of the cytodeme. Relationships among and within the species were studied using RAPDs, RFLPs, and DNA sequence comparisons. Intraspecific genetic variation in populations of wild B. oleracea from Britain, France, and Spain was explored using RAPDs. A considerable amount of variation existed but distinct differences between regions could not be discerned. Interspecific relationships were analyzed using random genomic and cDNA RFLPs. Populations could be clustered by species designation, except for one B. montana population. A tendency for the species to associate by geographical region was observed. Phylogenetic relationships were studied using a chloroplast DNA sequence. Ten different sequence variants, haplotypes, were found but they did not correspond to the species designations. Several species contained more than one haplotype while other species were found to contain the same haplotype. Parsimony analysis of DNA sequences showed that two haplotypes had diverged from the other species of the cytodeme but the rest of the haplotypes could not be resolved.
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