Feral populations of Brassica oleracea along Atlantic coasts in western Europe
Domestication revolutionised human societies and dramatically altered the evolutionary trajectories of domesticated species, including the classic example of cabbages (Brassica oleracea). Due to the agricultural importance of B. oleracea, issues related to food security, and the idea that crop wild relatives hold important genetic resources in situ, understanding the domestication history and genetics of wild cabbage populations has become economically, as well as scientifically, relevant. The origin of wild cabbage populations along Atlantic coasts remains unclear and a comprehensive genetic analysis of these potentially agriculturally useful populations is lacking. The main aim of this study was to characterise the population structure of geographically isolated wild cabbage populations along the coasts of the UK and Spain, including the Atlantic range edges. Double-digest restriction-site associated DNA26 sequencing was used to sample individual cabbage genomes, assess the similarity of plants from populations, and explore environment-genotype associations across varying climatic conditions. Interestingly, there were no indications of isolation-by-distance; several geographically close populations were genetically more distinct from each other than to distant populations. Furthermore, several distant populations shared genetic ancestry, which could indicate that they were established by escapees of similar source cultivars. There were signals of local adaptation to different environments, including a possible relationship between genetic diversity and soil pH. Overall, these results highlight wild cabbages in the Atlantic region as an important genetic resource worthy of further research and support the notion that they are feral populations recently expanded from domesticated sources.