The common bean (Phaseolus vulgaris L.) is the most important grain legume for direct human consumption, being especially important in eastern Africa and in Latin America. The objective of the Centro Internacional de Agricultura Tropical (CIAT) in participating in the Consultative Group on International Agricultural Research (CGIAR) Micronutrients Project has been to assess the feasibility of improving common beans for micronutrient content, especially iron and zinc. In the evaluation of more than a thousand accessions in the cultivated core collection, a mean iron concentration of 55 mg/kg was found, with a range of 34 to 89 mg/kg. Zinc concentrations ranged between 21 and 54 mg/kg, with an average value of 35 mg/kg. These initial data suggest that sufficient genetic variability exists to improve iron content by about 80% and zinc content by about 50%. An essential question for the improvement of any trait through plant-breeding is the degree to which the trait is stable across environments. Genetic differences have been expressed over environments and seasons, offering good prospects that genotypes selected in one environment for high iron or zinc will express superior levels of minerals in other environments as well. Correlations among mineral concentrations suggest that the improvement of one mineral may simultaneously improve the contents of other minerals, thus multiplying the impact of the effort. The fact that the bioavailability of iron was higher in white beans in rat studies suggests that a lower tannin content could be beneficial, but the role of tannin is still not well elucidated. The genetics of iron and zinc content appears to be complex, involving between 7 and 11 loci.

Landraces of common bean (Phaseolus vulgaris L.) pertaining to the Andean gene pool are remarkably diverse in plant and grain morphology and agroecological adaptation. The objectives of this study were to determine the genetic structure of a large sample of Andean landraces, and to establish a correspondence between Andean landraces and wild bean populations that might have served as the source of domesticated bean. A total of 182 landraces representing the three recognized races of Andean bean and including many popping bean types were analyzed using amplified fragment length polymorphism (AFLP) technology with multiple correspondence analysis (MCA) and unweighted pair group method with arithmetic mean (UPGMA). Twenty‐nine wild bean accessions representing the diversity of wild bean in South America and Middle America were also included. Two sets of primers were used to generate 189 polymorphic AFLP. The graph of the results of MCA indicated that most landrace accessions formed a single undifferentiated group, and analysis by UPGMA combined with bootstrapping confirmed this. A small number of outliers presented bands that suggested introgression from Mesoamerican beans. Among wild bean populations from South America, those from Bolivia graphed in closest proximity to the cultivated bean, suggesting that Bolivia might have been an important primary domestication site. The narrow genetic base of Andean beans emphasizes the need to broaden the genetic base of the Andean gene pool.

Iron and zinc deficiencies are human health problems found throughout the world and biofortification is a plant breeding-based strategy to improve the staple crops that could address these dietary constraints. Common bean is an important legume crop with two major genepools that has been the focus of genetic improvement for seed micronutrient levels. The objective of this study was to evaluate the inheritance of seed iron and zinc concentrations and contents in an intra-genepool Mesoamerican × Mesoamerican recombinant inbred line population grown over three sites in Colombia and to identify quantitative trait loci (QTL) for each mineral. The population had 110 lines and was derived from a high-seed iron and zinc climbing bean genotype (G14519) crossed with a low-mineral Carioca-type, prostrate bush bean genotype (G4825). The genetic map for QTL analysis was created from SSR and RAPD markers covering all 11 chromosomes of the common bean genome. A set of across-site, overlapping iron and zinc QTL was discovered on linkage group b06 suggesting a possibly pleiotropic locus and common physiology for mineral uptake or loading. Other QTL for mineral concentration or content were found on linkage groups b02, b03, b04, b07, b08 and b11 and together with the b06 cluster were mostly novel compared to loci found in previous studies of the Andean genepool or inter-genepool crosses. The discovery of an important new locus for seed iron and zinc concentrations may facilitate crop improvement and biofortification using the high-mineral genotype especially within the Mesoamerican genepool.

Legumes provide essential micronutrients that are found only in low amounts in the cereals or root crops. An ongoing project at CIAT has shown that the legume common bean is variable in the amount of seed minerals (iron, zinc, and other elements), vitamins, and sulfur amino acids that they contain and that these traits are likely to be inherited quantitatively. In this study we analyzed iron and zinc concentrations in an Andean recombinant inbred line (RIL) population of 100 lines derived from a cross between G21242, a Colombian cream-mottled climbing bean with high seed iron/zinc and G21078, an Argentinean cream seeded climbing bean with low seed iron/zinc. The population was planted across three environments; seed from each genotype was analyzed with two analytical methods, and quantitative trait loci (QTL) were detected using composite interval mapping and single-point analyses. A complete genetic map was created for the cross using a total of 74 microsatellite markers to anchor the map to previously published reference maps and 42 RAPD markers. In total, nine seed mineral QTL were identified on five linkage groups (LGs) with the most important being new loci on b02 and other QTL on b06, b08, and b07 near phaseolin. Seed weight QTL were associated with these on b02 and b08. These Andean-derived QTL are candidates for marker-assisted selection either in combination with QTL from the Mesoamerican genepool or with other QTL found in inter and intra-genepool crosses, and the genetic map can be used to anchor other intra-genepool studies.