Survey and genetic diversity of wild Brassica oleracea L. germplasm from the northern coast of Spain

This study follows from an expedition undertaken in 2011 to collect and monitor populations of Brassica oleracea var. oleracea growing on the Atlantic cliffs in the north of Spain. The genetic diversity and structure of 17 of these populations were analysed with Single Nucleotide Polymorphisms (SNP) revealed through Diversity Arrays Technology (DArT). These were compared with eight similar populations from the Atlantic coasts of northern Europe, with a representation of six Mediterranean wild taxa belonging to the Brassica oleracea complex and with six leafy kale landraces from Italy and Spain. The analysis reveals that the largest B. oleracea genetic diversity is present in the Asturias region. Another evidence is the presence of a north-south gradient of diversity along the Atlantic coasts, and the distinction between two types of accessions, one confined to northwest Spain ('AsCan' type) and another comprising most northern populations and the cultivated leafy kales, with an intermediate area of admixed types. The genetic distance among all the B. oleracea var. oleracea populations and between these and the leafy kales is minimal. This brings further weight to the interpretation of the wild-growing Atlantic populations of B. oleracea as a feral group. A specific pivotal position is assigned to the population of Laredo, Cantabria, which is genetically very close to 63% of the other accessions. In this study, Brassica incana is genetically the closest wild taxon to cultivated leafy kales and feral B. oleracea, and thus is indicated as a possible source of domestication of B. oleracea.