Drought-Induced Phenotypic Differences in Symbiotic Nitrogen Fixation in Common Bean.

Common bean (Phaseolus vulgaris L.) is a major food legume in Latin America and Africa. Bean yields are limited by drought stress during crop development and drought stress markedly reduces nodulation and symbiotic nitrogen fixation (SNF). Phenotypic variation in SNF capacity could provide the potential to breed for increased SNF, even under terminal drought conditions. Research was conducted at the International Center for Tropical Agriculture (CIAT) in Colombia from 2012 to 2013 to identify phenotypic differences in SNF among 16 parental genotypes used in CIAT’s common bean breeding program. The genotypes were grown in both well-watered and rainfed conditions to examine their responses to differences in water availability. At mid-pod filling growth stage, canopy biomass samples were collected, dried, ground, and stable N isotope concentrations were determined. For the calculation of nitrogen derived from the atmosphere (Ndfa), two non-nodulating genotypes were included in the trials. Reduced yields and reduced SNF were found under rainfed versus well-watered conditions. Importantly, significant phenotypic variation in Ndfa was also identified. These results suggest that the existing phenotypic variation can be utilized to breed and select for improved SNF and yield under drought stress.