Genetic diversity at isozyme and RFLP loci in Brassica campestris as related to crop type and geographical origin.

Twenty accessions of Brassica campestris, representing the major crop types and their geographical origin, were tested for gene frequency at five isozyme and four RFLP loci. The majority of alleles (67%) were found in all geographic regions. Nearly 3 times more alleles were detected at RFLP loci than at isozyme loci. Genetic diversity among crop types (with the exception of turnip) was similar to diversity estimates of geographical regions, implying that crops used for similar purposes (i.e., oilseed or leafy vegetable) are derived from geographically differentiated populations. Geographically, Central Asian and Indian types showed the highest level of heterozygosity (excluding self-fertile sarson oilseed types), followed closely by European varieties, and Asian varieties showed the greatest gene diversity. Phenetic dendrograms indicated that sarson and Chinese cabbage have diverged considerably from other types, perhaps due to consequences of their breeding habit or origin.