Brassica rapadomestication: untangling wild and feral forms and convergence of crop morphotypes

AbstractThe study of domestication contributes to our knowledge of evolution and crop genetic resources. Human selection has shaped wildBrassica rapainto diverse turnip, leafy, and oilseed crops. Despite its worldwide economic importance and potential as a model for understanding diversification under domestication, insights into the number of domestication events and initial crop(s) domesticated inB. rapahave been limited due to a lack of clarity about the wild or feral status of conspecific non-crop relatives. To address this gap and reconstruct the domestication history ofB. rapa, we analyzed 68,468 genotyping-by-sequencing-derived SNPs for 416 samples in the largest diversity panel of domesticated and weedyB. rapato date. To further understand the center of origin, we modeled the potential range of wildB. rapaduring the mid-Holocene. Our analyses of genetic diversity acrossB. rapamorphotypes suggest that non-crop samples from the Caucasus, Siberia, and Italy may be truly wild, while those occurring in the Americas and much of Europe are feral. Clustering, tree-based analyses, and parameterized demographic inference further indicate that turnips were likely the first crop type domesticated, from which leafy types in East Asia and Europe were selected from distinct lineages. These findings clarify the domestication history and nature of wild crop genetic resources forB. rapa, which provides the first step toward investigating cases of possible parallel selection, the domestication and feralization syndrome, and novel germplasm forBrassicacrop improvement.