Structure and Genetic Diversity of Wild Populations of Lima Bean (Phaseolus lunatus L.) from the Yucatan Peninsula, Mexico

Abstract

This study was conducted to determine the genetic diversity, structure and gene flow of 11 wild populations of Phaseolus lunatus L. in four regions of traditional agriculture in the Yucatan Peninsula, Mexico, part of the putative domestication area of its Mesoamerican gene pool. Analyzing eight microsatellite loci, the populations showed high values of diversity: observed heterozygosity (Ho) 0.46 to 0.9; Nei's index of diversity (H) 0.35 to 0.59 and average number of alleles per locus (A) 2.37 to 3.38. Both Nei's index of populations differentiation (Gst) and analysis of molecular variance (AMOVA) indicated strong differentiation. The Bayesian analysis of grouping and the Mantel test suggested isolation among agricultural regions as a major factor for population differentiation. Even though a low long-term gene flow (Nm 5 0.66) and low rates of recent migration among populations were observed, there were some cases where the accidental transport of seeds could be favoring a gene flow at a long distance. Data found in this study suggest a positive correlation between agricultural intensification and increase in diversity, suggesting that wild populations are favored by the intensification of disturbance in situations involving at least 3 yr of fallow. However, the opposite could be true at higher levels of intensification as has been reported in the Central Valley of Costa Rica, where the diversity is diminishing.

Differentiation and genetic diversity of Phaseolus lunatus wild populations from Chiapas, Mexico, and their genetic relationships with MI and MII groups

“…In Phaseolus lunatus, selfing is favored by the synchronized maturation of pollen grains and stigma and by their proximity within the flower bud (Webster et al 1979). The F IS value found in Chiapas contrasts with the value reported by Martínez-Castillo et al (2006) for the Yucatan Peninsula (F IS = -0.31). These differences in F IS between both regions of Mexico appear to correspond to the difference in the size the populations and the levels of endogamy, and it can be another factor to explain the greater differentiation in the P. lunatus wild populations from Chiapas.…”

“…It has been noted that the founder effect associated with recolonization increases the differentiation between subpopulations (Wright 1977). Although all these factors can lead to isolation by distance, our Mantel analysis was not significant and thus did not indicated the existence of such geographical isolation, which has previously been reported for the species (Martínez-Castillo et al 2006, Serrano-Serrano et al 2010. One possible explanation for this result is the existence of admixed accessions, namely accessions possessing ancestry derived from more than one accession as a result of recent gene flow.…”

“…The observed genetic differentiation between wild accessions of P. lunatus from Chiapas was higher than that reported for the Yucatan Peninsula region using also SSR markers (F ST = 0.27, Martínez-Castillo et al 2006). It is important to highlight that, compared with the Yucatan Peninsula, the territory of Chiapas is much more heterogeneous, with mountains, valleys, different climates and soils that favors the existence of geographical barriers that limit gene flow.…”

“…Although historical gene flow (Nm) was not directly assessed in this study, the natural dispersion of P. lunatus wild populations by dehiscence of the sheath limits the radius of maximum dispersal of seeds (six meters) favoring low Nm values (Baudoin et al 2004). Several studies have reported low Nm values (less than 1) for wild populations of this species (Ouédraogo & Baudoin 2002, Martínez-Castillo et al 2006.…”

“…These markers have proved a useful tool for determining the genetic structure in many plant species (Mattioni et al 2013, Lavor et al 2014, Noormohammadi et al 2014, Shivaprakash et al 2014. In wild Phaseolus lunatus, SSRs have been used to determine the genetic structure in populations of Costa Rica and Mexico, showing high genetic differentiation between wild populations of P. lunatus and clustering patterns based on geographical isolation and low levels of gene flow (Ouédraogo et al 2005, Martínez-Castillo et al 2006.…”