Diversity in natural populations of wild Brassica oleracea as estimated by isozyme and RAPD analysis

Abstract

Naturally occurring populations of wild Brassica oleracea were collected in Spain, France, and Great Britain. Allele frequencies at four isozyme loci were determined for 18 populations, while five populations were screened using five random primers to generate RAPDs. Levels of homozygosity and gene diversity, H, were computed for each population using isozyme data and RAPD data when applicable. Homozygosity levels tended to be higher in smaller populations, which could also be observed as increased numbers of homozygous loci in smaller populations. Gene diversity values based on isozymes indicated considerable within population variation regardless of population size. The RAPID based gene diversities were significantly higher and the two exceptional populations displayed diversity levels more in keeping with the rest. The coefficient of gene differentiation, G ST , for populations in each region showed that the Spanish populations were more homogenous than the French or British. When the G ST for all populations was calculated using isozymes vs. RAPD data, the RAPD data gave a significantly lower value, a plausible result of the higher within population variation detected using RAPDs. Genetic distances between populations from different regions were also calculated from both data sets and used to produce phenograms. Clustering according to geographic region was not evident using either isozyme or RAPD data.