Genetic and Morphological Diversity in Spontaneous Populations of Brassica rapa: How Do Feral Populations Differ From...

Crop wild relatives are a valuable source of genetic material for improving cultivated crops. However, feral populations-self-sustaining plants that have escaped cultivation-are often mistaken for wild relatives because they exhibit traits such as seed dispersal and dormancy, which resemble wild forms and support persistence in natural habitats. This study examined the genetic diversity, population structure, and morphology of 117 Brassica rapa populations, including landraces from farms or genebanks and spontaneous populations sampled in the wild across the Mediterranean basin. Substantial genetic diversity was observed in the 45 wild populations from Italy and Algeria, with clear genetic differentiation from cultivated landraces. In contrast, spontaneous populations in France and Slovenia showed reduced diversity, comparable to that of landraces, and clustered closely with them in genetic analyses. Population trees and admixture analyses showed that the French spontaneous populations were more closely related to other landraces than to any other wild populations, which confirmed their feral origin. We also identified the most likely landrace ancestor for each feral population, which pointed towards a French landrace in nearly all cases. These findings support previous evidence that most European B. rapa populations are feral rather than truly wild. Morphological analyses further showed that feral populations displayed traits intermediate between wild and cultivated groups and even suggested some reversion towards pre-domestication traits in root morphology and germination. This highlights how feralisation can blur distinctions between wild relatives and crop escapes. Overall, the study emphasizes the need to disentangle wild and feral populations when identifying genetic resources for breeding. Further research is required to clarify the history of feralisation in B. rapa, including the origins and spread of populations, gene flow with crops and wild relatives, and the role of local adaptation in shaping their persistence.