Influence of nitrogen supply on gas exchange, chlorophyll fluorescence and grain yield of breeding lines of common bean evaluated in the Amazon region of Colombia

The common bean ( Phaseolus vulgaris L.) is a food crop that provides fiber, vitamins and carbohydrates and it is produced by smallholders in developing countries under nitrogen (N)-depleted and low-fertility soil conditions. Soil acidity and the associated aluminum toxic and phosphorus deficient conditions are known to reduce symbiotic N-fixing ability of common bean. Breeding lines of common bean have been developed to adapt to acid-soil and high-temperature conditions in the Amazon region but the response of these lines to N application was not determined. The present study was conducted with an objective to identify genotypic differences among ten common bean breeding lines (4 Andean, 5 Mesoamerican, 1 interspecific) in their physiological characteristics (gas exchange, chlorophyll fluorescence and photosynthetic efficiency) and their contribution to superior agronomic performance under three different levels of N (0, 60 and 120 kg N ha −1 ; N0, N60 and N120) supply. We tested the hypothesis that common bean genotypes that combine greater capacity to assimilate carbon with improved ability to mobilize photosynthates to developing pods and seeds could enhance their agronomic performance at different levels of N supply under high-temperature and acid soil-stress conditions in the field. A randomized complete block design with factorial arrangement (3 levels of N × 10 genotypes) in three replications was used for the study. Measurements included photosynthetic gas exchange characteristics (light and CO 2 -saturated photosynthesis), chlorophyll fluorescence, viability of pollen, leaf N concentration, photosynthetic N use efficiency and grain yield. The increase in supply of N had a significant effect on grain yield and on different photosynthetic characteristics. Results showed that lines with indeterminate growth habit responded better to increase in N supply through their physiological response in improving grain yield. Among the genotypes evaluated, two lines (BFS 10 and SEF 10) were outstanding in their agronomic performance due to greater photosynthetic capacity combined with greater ability to mobilize photosynthates to grain with increase in N supply. These two lines can serve as parents for further improvement in resource use efficiency and multiple-stress resistance of common bean in the tropics.