The Evolutionary History of Wild, Domesticated, and Feral Brassica oleracea (Brassicaceae)

Authors: MABRY, MACKENZIE - University Of Missouri; HISSONG, SARAH - University Of California, Davis; GALLAGHER, EVAN - University Of Missouri; AN, H - University Of Missouri; Labate, Joanne; GORE, MICHAEL - Cornell University; PIRES, CHRIS - University Of Missouri

Submitted to: Molecular Biology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/3/2021
Publication Date: 6/22/2021
Citation: Mabry, M.E., Hissong, S.D., Gallagher, E.Y., An, H., Labate, J.A., Gore, M.A., Pires, C.J. 2021. The Evolutionary History of Wild, Domesticated, and Feral Brassica oleracea (Brassicaceae). Molecular Biology and Evolution. https://doi.org/10.1093/molbev/msab183.
DOI: https://doi.org/10.1093/molbev/msab183

Interpretive Summary: Cole crops are estimated to be worth more than $1.8 million in US annual market value. Cole crops are all very closely related to each other and include many crop types including broccoli, Brussels sprout, cabbage, kale, and kohlrabi, as well as several lesser well-known types, such as walking stick kale and marrow cabbage. However, very little is known about the original development of these types. Based on uncertainty of the closest wild plant relatives of these crops, several conflicting ideas on geographic origins have been proposed. Some evidence suggests an Italian origin, as there is a large diversity of wild relatives there, while others suggest England as the location of origin. By DNA sequencing a set of 225 varieties representing 19 different Cole crop types and eight different wild relatives, the closest wild relatives were identified. Results supported the origin of cultivation in the Mediterranean region. These results help further the understanding of genetic relationships needed for continued improvement of this highly diverse and nutritionally valuable set of vegetable crops.

Technical Abstract: Brassica oleracea is an important crop species that has intrigued researchers for centuries. When first introduced to the species, Darwin drew many parallels between his theory on natural selection and the domestication practices that led to the varied forms of this plant. Brassica oleracea is unique in that it has been domesticated into several different crop types, including broccoli, Brussels sprouts, cabbage, kale, and kohlrabi, as well as several lesser well-known types, such as walking stick kale and marrow cabbage. However, over a century and a half after Darwin, we still know very little about this crop species. Based on uncertainty of the wild relatives of this species, several conflicting hypotheses on the geographic origin have been proposed. Some evidence suggests a Sicilian origin, as there is a large diversity of wild relatives there, while others suggest England as the location of origin, however these are more likely feral populations of once domesticated cabbage. Using a diversity panel of 225 accessions from 19 different B. oleracea crop types and eight species of potential wild relatives, we integrate phylogenetic and populations genetic techniques to examine patterns of relationships among domesticated types and wild relatives. These analyses point to the closest living relatives of B. oleracea as B. incana and B. cretica, indicating support for origin of cultivation in the Mediterranean region, and recover evidence for multiple origins of kales. Together, these results put us one step closer to further understanding the evolutionary history of these fascinating and important crops.