Genetic Structure and Mating Systems in Wild and Cultivated Populations of Phaseolus coccineus and P. vulgaris (Fabaceae)

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We present a study of the genetic variation, genetic structure, and outcrossing rate of two wild populations of Phaseolus coccineus ssp. formosus (both from Central Mexico), two cultivated populations of P. coccineus ssp. coccineus (one from Central Mexico, the other from Chiapas), and one cultivated population of P. vulgaris (from Central Mexico), using seven electrophorectic loci. All the populations of P. coccineus showed high and similar levels of genetic variation, without differences among wild and cultivated populations (H ranged between 0.187 to 0.271). In contrast, P. vulgaris has low levels of genetic variation (H = 0.041). The three P. coccineus populations from Central Mexico were genetically similar, while the cultivated P. coccineus from Chiapas and the cultivated P. vulgaris from Central Mexico were very different. In all the loci and all the populations for both species, the fixation indices (F) were positive and differed significantly from random mating expectation in 59% of the cases for P. coccineus. The highest F was the estimated for P. vulgaris. For P. coccineus, the multilocus outcrossing rate estimates ranged from 0.592 to 0.698, and these did not differ significantly among populations. For P. coccineus, we also estimated the outcrossing rate for each of 60 different families, showing great variation, with a majority of families with a t between 0.8 and 1, but a substantial fraction of the families with a t as low as 0.12–0.20. The domestication process has neither eroded the levels of genetic variation of the cultivated populations of P. coccineus nor changed its mating system.

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