Phenotypic selection in weedy radish and its bidirectional crop–weed hybrids across two contrasting environments

Hybridization is a key mechanism in the adaptive evolution of weeds and invasive species. The evolutionary success of hybrids may be shaped by selection on functional traits, interacting with maternal genotype and ecological context. We performed experimental hybridization and common garden field experiments to assess phenotypic variation on functional traits, and the strength and direction of linear and quadratic selection acting on them, in bidirectional crop-weed hybrids and their parents of <i>Raphanus sativus</i>, across two contrasting environments: agrestal (agricultural) and ruderal (human-disturbed uncultivated area), over two years. Bidirectional hybrids exhibited overall greater values for size-related traits than their parents, with similar flowering time and no significant effects of cross direction. Selection acted on multiple functional traits through both linear and quadratic components, with broadly similar patterns across environments and cross types, although selection tended to be slightly stronger in hybrids than in weeds. Intraspecific crop-weed hybridization, regardless of cross direction, can increase weediness in weedy radish by enhancing plant size, thereby increasing competitive ability and potential interference with crops. Our findings highlight how hybridization and selection shape plant evolution, influencing the potential introgression of crop alleles into wild or weedy gene pools. Understanding the hybridization process and the mechanisms that control it is crucial for managing the evolutionary outcomes of crop-weed hybridization.