Wild Papaya Shows Evidence of Gene Flow from Domesticated Maradol Papaya in Mexico

Multiple factors threaten the conservation of crop wild relatives (CWR), such as habitat transformation and fragmentation, rapid environmental changes, introduction of invasive species, urbanization, and introduction of genetically modified organisms. Moreover, in regions where CWR coexist with their domesticated counterparts, reductions of genetic diversity and local extinction of wild populations due to homogenization in allelic frequencies, are expected. Nowadays, papaya plantations in Mexico extend over large areas including the natural distribution of its wild relative, potentially favoring genetic exchange between wild and domesticated plants. In this study, we evaluated the potential distribution of wild papaya and analyzed the genetic diversity and structure, using microsatellites and cpDNA markers, to identify the evolutionary units and possible events of gene flow within the wild-to-domesticated complex of papaya, including conventional and transgenic domesticated plants in Mexico. The potential distribution showed a good climatic suitability for the tropical regions of the Pacific coast, the Gulf of Mexico and the Yucatan Peninsula. We identified large evolutionary units for wild plants and evidence of gene flow from papaya plantations to wild units. Wild papaya units in the vicinity of papaya plantations showed reduced genetic diversity, owing to the highly reduced genetic diversity in domesticated plants. No evidence was found of the presence of transgenes in wild populations and plantations of papaya throughout Mexico. Our findings raise concerns about the maintenance of CWR gene pools and the need for improved management and conservation strategies for Carica papaya in its center of origin, domestication and diversification.