The role of intraspecific crop–weed hybridization in the evolution of weediness and invasiveness: Cultivated and weedy radish (Raphanus sativus) as a case study

Abstract

Premise: The phenotype of hybrids between a crop and its wild or weed counterpart is usually intermediate and maladapted compared to that of their parents; however, hybridization has sometimes been associated with increased fitness, potentially leading to enhanced weediness and invasiveness. Since the ecological context and maternal genetic effects may affect hybrid fitness, they could influence the evolutionary outcomes of hybridization. Here, we evaluated the performance of first-generation crop–weed hybrids of Raphanus sativus and their parents in two contrasting ecological conditions. Methods: Using experimental hybridization and outdoor common garden experiments, we assessed differences in time to flowering, survival to maturity, plant biomass, and reproductive components between bidirectional crop–weed hybrids and their parents in agrestal (wheat cultivation, fertilization, weeding) and ruderal (human-disturbed, uncultivated area) conditions over 2 years. Results: Crop, weeds, and bidirectional hybrids overlapped at least partially during the flowering period, indicating a high probability of gene flow. Hybrids survived to maturity at rates at least as successful as their parents and had higher plant biomass and fecundity, which resulted in higher fitness compared to their parents in both environments, without any differences associated with the direction of the hybridization. Conclusions: Intraspecific crop–weed hybridization, regardless of the cross direction, has the potential to promote weediness in weedy R. sativus in agrestal and ruderal environments, increasing the chances for introgression of crop alleles into weed populations. This is the first report of intraspecific crop–weed hybridization in R. sativus.