ORIGINAL ABSTRACT

Feralization is an evolutionary process that can reverse domestication traits, giving rise to invasive or weedy plants. Brassica rapa is an example of extensive diversification, producing multiple domesticated crops, while its non-crop forms persist as weeds in disturbed habitats worldwide. In Argentina, the spread of this weed has increased since 2012, when populations resistant to glyphosate (transgenic) and to acetohydroxyacid synthase (AHAS)-inhibiting herbicides (non-transgenic) were first reported. Despite their spread across more than one million hectares with economic consequences, their origin and genetic diversity remain unknown. This study aims to evaluate the genetic diversity and population structure of Argentinian B. rapa accessions and try to infer the origin of herbicide-resistant populations. We analysed 56 Argentinian accessions and compared them with 568 accessions worldwide using genotyping-by-sequencing. A total of 15 790 SNPs were used to analyse genetic diversity, population structure, and phylogeny. Resistant and susceptible Argentinian accessions formed a genetically homogeneous group distinct from global populations. An exception was a population from southwestern Argentina, which clustered separately. The lowest genetic differentiation was observed with weedy strains from South and North America and with European turnips, suggesting a shared origin and local differentiation. The genetic similarity between resistant and susceptible accessions suggests that herbicide resistance may have emerged via local gene flow from transgenic Brassica napus cultivated informally in Argentina. Overall, our findings improve understanding of the genetic diversity and evolutionary history of this weed and provide a genomic baseline for future management strategies, as well as insights into transgene escape.