Variation and population structure at microsatellite and isozyme loci in wild cabbage (Brassica oleracea L.) in Dorset (UK)

We examined variation at four isozyme and seven microsatellite loci in natu ral populations of Brassica oleracea L. on the coast of Dorset. All loci we re polymorphic, and the diversity index of isozyme loci was similar to that of the microsatellites. Both microsatellites and isozymes showed significa nt spatial differentiation of genetic variation, but the scale differed bet ween the marker types. Significant non-random mating at isozyme loci was de tected within small groups of about five plants, in which adjacent individu als were separated by less than 5 m. On the other hand, non-random mating a t microsatellite loci was only detected within the Dorset region as a whole . F-ST was significant for all loci and there was evidence of isolation by distance at both microsatellite and isozyme loci. From these data we infer that there is low but significant amounts of gene flow among B. oleracea po pulations in Dorset. The differences in the genetic structure between the t wo types of marker may be due to higher mutation rates at the microsatellit e loci; however, the data suggest that stepwise gain or loss of single repe at units is not the principal mechanism.