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Abstract:
The scarlet runner bean (Phaseolus coccineus) is one of the five domesticated Phaseolus species. It is cultivated in small-scale agriculture in the highlands of Mesoamerica for its dry seeds and immature pods, and unlike the other domesticated beans, P. coccineus is an open-pollinated legume. Contrasting with its close relative, the common bean, few studies focusing on its domestication history have been conducted. Demographic bottlenecks associated with domestication might reduce genetic diversity and facilitate the accumulation of deleterious mutations. Conversely, introgression from wild relatives could be a source of variation. Using Genotyping by Sequencing data (79,286 single-nucleotide variants) from 237 cultivated and wild samples, we evaluated the demographic history of traditional varieties from different regions of Mexico and looked for evidence of introgression between sympatric wild and cultivated populations. Traditional varieties have high levels of diversity, even though there is evidence of a severe initial genetic bottleneck followed by a population expansion. Introgression from wild to domesticated populations was detected, which might contribute to the recovery of the genetic variation. Introgression has occurred at different times: constantly in the center of Mexico; recently in the North West; and anciently in the South. Several factors are acting together to increase and maintain genetic diversity in P. coccineus cultivars, such as demographic expansion and introgression. Wild relatives represent a valuable genetic resource and have played a key role in scarlet runner bean evolution via introgression into traditional varieties.
