Looking for a common bean ideotype with high photosynthesis and water-use efficiency under light fluctuation

High crop yield is needed to feed the global population but limiting environmental conditions constrain food production. Since high photosynthesis and water-use efficiency are two key traits for crop yield in a changing world, we aimed to evaluate the photosynthetic performance and stomatal dynamics of twenty-six common bean genotypes under fluctuating light. Leaf gas exchange and chlorophyll fluorescence were evaluated on the middle leaflet of the first fully expanded leaf during high-low-high light transitions. Photosynthetic response curves to increasing light were also performed and key photosynthetic traits estimated. Seventeen physiological traits explained 94.5 % of the variation among common bean genotypes. Significant variability for photosynthesis, stomatal conductance and water-use efficiency was observed both during light fluctuation and under light saturation. TAA Dama, ANFC9, IAC Veloz and IPR Urutau presented the highest photosynthetic capacity to increasing light availability. Furthermore, IAC Sintonia, IAC2156 and IAC2157 were the most water-use efficient cultivars, due to their stomatal sluggishness and asynchronous behaviour between stomatal conductance and photosynthesis. The genetic diversity for photosynthesis and stomatal conductance found in this study provides the basis for breeding and illustrates the potential of exploiting natural variation for increasing photosynthesis and yield while optimizing water-use efficiency.