Survey and genetic diversity of wild Brassica oleracea L. germplasm on the Atlantic coast of France

Wild populations of Brassica oleracea subsp. oleracea growing on European Atlantic coasts deserve attention since their diversity could contribute useful alleles to the Brassica oleracea cole crops (cabbage, broccoli, cauliflower, etc.). These populations have also been proposed as the source from which cole crops have been domesticated. Other authors have challenged their natural origin and suspected their derivation from vegetable brassicas escaped from fields and gardens. Our study surveyed northwestern French coastal areas and analysed with Amplified Fragment Length Polymorphism (AFLP) markers the genetic diversity and structure of nine wild populations, as well as of five accessions of locally grown B. oleracea crops. This study offered the highest level of detail ever presented about the distribution of wild B. oleracea populations along the French Atlantic coast. Populations analysed showed a low level of genetic differentiation, which might be explained by a relatively recent origin of all the populations from a common source, more likely than by insufficient physical or distance barriers to intercrossing. Traditional varieties commonly grown in the same area were not fully distinguishable from the wild populations on a molecular level. The level of genetic diversity of the wild populations was similar to, or lower than that of the cultivated crops. Therefore, the absence of a domestication bottleneck invited us to exclude the wild French populations as the likely source of original domestication events. Populations with higher levels of genetic diversity that could be targeted for conservation and breeding were the wild Penly and Petites Dalles and the Saint-Saëns cabbage.