Insight Into the Genetic Architecture of Local (Mal)Adaptation in Wild and Feral Brassica rapa Populations.

As climate change drives rapid environmental shifts, crops face significant challenges due to their limited adaptive genetic diversity, threatening food security. Crop wild relatives and potentially feral populations can serve as valuable reservoirs of adaptive diversity for breeding. Exploring and conserving this diversity is therefore essential, as it may encompass a wide range of adaptations. In this study, we investigate the genetic basis of local climate adaptation and the risk of maladaptation under future conditions in spontaneous populations-naturally occurring in the wild-of Brassica rapa (field mustard). A total of 62 populations were sampled, revealing strong differentiation between feral (France, Slovenia) and wild (Algeria, Sicily) populations. A genome-environment association analysis identified genomic regions associated with climatic variables, with broader patterns suggesting a polygenic architecture. Feral populations broadened the climatic range explored, but their reduced genetic diversity limited our ability to capture the full spectrum of adaptive variation in wild populations, indicating that the genetic architecture of climate adaptation is only partly shared between the two groups. We also used genomic offset (GO) analyses to assess mismatches between current and predicted-optimal genetic composition under 2050 climate projections. A common garden experiment indicated that GO captures some component of fitness variation, with feral populations providing additional predictive information beyond the environmental space occupied by wild populations. These findings highlight the complex genetic architecture of climate adaptation in B. rapa, as well as the potential and limitations of genomic tools for guiding conservation and crop improvement under climate change.