Genetic Relationships and Molecular Signatures of Divergence in Traditional Landraces and Morphotypes of Brassica oleracea

<i>Brassica oleracea</i> is a complex species incorporating a great variety of vegetable types, including cabbage, cauliflower, broccoli, kale, and others. Southern Italy, and especially the Puglia region, is rich in <i>B. oleracea</i> landraces. In this study, genotyping-by-sequencing (GBS) was applied to a germplasm panel of 82 samples, mostly landraces and some commercial varieties, belonging to various morphotypes of <i>B. oleracea</i>. Population structure (K = 2), principal component (PCA), and phylogenetic analyses resulted in a general subdivision of our samples into two large lineages: the types used for their leaves (LHL) and those consumed for their flower heads (AIL). Going deeper inside, the different morphotypes were mostly grouped into specific clusters, and a clear separation of particular landraces, such as the Mugnoli and Cima nera broccoli, was observed in the structure analysis (K = 7), as well as in the PCA and in the Neighbor-Joining tree. The calculation of the pairwise fixation index (F<i>_ST</i>, threshold > 0.50) between LHL and AIL types (based on population structure analysis at K = 2) provided 456 outlier single nucleotide polymorphisms (SNPs). Among the corresponding orthologs annotated in <i>Arabidopsis</i>, we identified several genes involved in flower/inflorescence development, cellular proliferation, etc. Overall, our investigation provides useful information on the knowledge of early domesticated landraces of <i>B. oleracea</i> and allows for the attribution of unknown material to the appropriate taxonomical ranking. The analysis of outlier SNPs has highlighted signatures of molecular divergence between LHL and AIL lineages.