Abstract
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.