Extensive diversity and inter-genepool introgression in a world-wide collection of indeterminate snap bean accessions

Abstract

Common bean can be grown as a grain crop (dry beans) or as a fresh vegetable (snap beans/green beans), both items being important in nutritional terms for providing essential minerals and vitamins to the diet. Snap beans are thought to be derived predominantly from dry beans of the Andean genepool and to be of a recent European origin; however, the existence of Mesoamerican genepool characteristics especially in traditional indeterminate growth habit snap beans indicates a wider origin. The objective of this study was to evaluate genetic diversity within a set of 120 indeterminate (pole type) snap beans and 7 control genotypes representing each genepool using amplified fragment length polymorphism (AFLP) and simple sequence repeat or microsatellite (SSR) markers. The genotypes were predominantly from Asia, Europe and the United States but included some varieties from Latin America and Africa. AFLP polymorphism ranged from 53.2 to 67.7% while SSR polymorphism averaged 95.3% for the 32 fluorescent and 11 non-fluorescent markers evaluated and total expected heterozygosity was higher for SSR markers (0.521) than for AFLP markers (0.209). Both marker systems grouped the genotypes into two genepools with Andean and Mesoamerican controls, respectively, with the Mesoamerican group being predominant in terms of the number of genotypes assigned to this genepool. Phaseolin alleles were not tightly associated with genepool assignment indicating that introgression of this locus had occurred between the genepools, especially with phaseolin "S" in the Andean group (23.5%) and phaseolins "T" and "C" in the Mesoamerican group (12.2 and 8.2%, respectively). The implications of these results on the origin of pole type snap beans and on breeding strategies for this horticultural crop are discussed.

Agro-morphological characterization and genetic divergence assessment in bush snap bean genotypes1

“…Better evidence of this clustering pattern is the phaseolin alleles pattern detected in genotypes already evaluated in other studies, such as Kentucky Wonder and Blue Lake-derived cultivars, belonging to a subgroup within the Mesoamerican genepool (Blair et al 2010). As observed in this study, such cultivars of smaller seeds were allocated to cluster I (Table 6).…”

“…So, as most the snap bean genotypes from different countries of origin tended to cluster together, similar germplasm may have been shared between countries, possibly due to strong trans-national seed exchange. In the literature, there is some evidence for snap bean ancestry having both Mesoamerican and Andean origins, especially regarding the existence of large seed size variability, which is associated with the phaseolin allele pattern (Myers & Baggett 1999, Blair et al 2010). According to these authors, the intense selection pressure for seed size in snap beans, in parallel to the selection for seed types in dry beans, freed the phaseolin alleles to introgress from one genepool to another.…”

“…However, snap beans are widely distributed and very diverse around the world, especially in Europe and Asia (Blair et al 2010).…”

“…Snap beans are also very diverse in growth habit and plant ideotype, ranging from type I (determinate) erect bush beans to type IV (indeterminate) climbing beans (Myers & Baggett 1999). The majority of tropical cultivars are indeterminate climbing snap beans, while determinate erect bush beans prevail in temperate zones (Blair et al 2010). In Brazil, for example, the main recommended snap bean cultivars are indeterminate-type crops, grown on trellises.…”

<b>AFLP analysis of genetic diversity in determinate and indeterminate snap bean accessions

“…The snap bean (Phaseolus vulgaris L.) is considered one of the most important vegetable crops worldwide, and it is relatively rich in vitamins, minerals and antioxidants (Abu-Reidah, Arráez-Román, Lozano-Sánchez, Segura-Carretero, & Fernández-Gutiérrez, 2013;Blair, Chaves, Tofiño, Claderón, & Palacio, 2010). The estimated production of snap bean worldwide is approximately 21 million tons, and China, Indonesia, India and Turkey are the largest producers, according to data from the Food and Agriculture Organization of the United Nations (FAO, 2014 In Brazil, data on snap bean production and market relevance are scarce, given the lack of reliable statistics and systematized information.…”