Abstract
Evolutionary studies that are aimed at defining the processes behind the present level and organization of crop genetic diversity represent the fundamental bases for biodiversity conservation and use. A Mesoamerican origin of the common bean Phaseolus vulgaris was recently suggested through analysis of nucleotide polymorphism at the nuclear level. Here, we have used chloroplast microsatellites to investigate the origin of the common bean, on the basis of the specific characteristics of these markers (no recombination, haploid genome, uniparental inheritance), to validate these recent findings. Indeed, comparisons of the results obtained through analysis of nuclear and cytoplasmic DNA should allow the resolution of some of the contrasting information available on the evolutionary processes. The main outcomes of the present study are: (i) confirmation at the chloroplast level of the results obtained through nuclear data, further supporting the Mesoamerican origin of P. vulgaris, with central Mexico representing the cradle of its diversity; (ii) identification of a putative ancestral plastidial genome, which is characteristic of a group of accessions distributed from central Mexico to Peru, but which have not been highlighted beforehand through analyses at the nuclear level. Finally, the present study suggests that when a single species is analyzed, there is the need to take into account the complexity of the relationships between P. vulgaris and its closely related and partially intercrossable species P. coccineus and P. dumosus. Thus, the present study stresses the importance for the investigation of the speciation processes of these taxa through comparisons of both plastidial and nuclear variability. This knowledge will be fundamental not only from an evolutionary point of view, but also to put P. coccineus and P. dumosus germplasm to better use as a source of useful diversity for P. vulgaris breeding.
Highlights
The wild forms of the common bean Phaseolus vulgaris grow across a wide geographic area of the Americas, from northern Mexico to northwestern Argentina (Toro et al, 1990)
This hypothesis was the most credited until the study of Bitocchi et al (2012) that analyzed the genetic diversity at five nuclear gene fragments across a wide sample of wild P. vulgaris accessions, where they showed that the wild forms of P. vulgaris originated in Mesoamerica, and most likely in central Mexico
These five gene fragments include four legume anchor (Leg) markers, developed by Hougaard et al (2008), and one gene fragment, PvSHP1, developed by Nanni et al (2011); PvSHP1 is a homolog of the SHATTERPROOF (SHP1) gene, which is involved in the control of fruit shattering in Arabidopsis thaliana
Summary
The wild forms of the common bean Phaseolus vulgaris grow across a wide geographic area of the Americas, from northern Mexico to northwestern Argentina (Toro et al, 1990). Morphological, biochemical, and molecular data have indicated that the wild populations from Mexico, Central America, and Colombia differ from those of southern Peru, Bolivia, and Argentina (Gepts et al, 1986; Delgado-Salinas et al, 1988; Koenig and Gepts, 1989; Gepts and Debouck, 1991; Becerra-Velásquez and Gepts, 1994; Papa and Gepts, 2003; Angioi et al, 2009a; Kwak and Gepts, 2009; Rossi et al, 2009) These two groups represent two geographically distinct and isolated gene pools (Mesoamerica and Andes, respectively) that were already present before domestication of the common bean (for reviews, see Papa et al, 2006; Bitocchi et al, 2012, 2013). This conclusion was suggested by the evidence of a bottleneck that occurred in the Andes prior to domestication (Rossi et al, 2009; Nanni et al, 2011; Bitocchi et al, 2012) and to the presence of high genetic structure in Mesoamerica (Bitocchi et al, 2012), with the different genetic groups identified having diverse relationships with the wild populations from northern Peru and Ecuador and from the Andes
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