Association of nodule performance traits with shoot performance traits of Common Bean under drought stress

Summary

Although symbiotic nitrogen fixation (SNF) and nodule characteristics have been evaluated before, their use as phenotypic markers for drought tolerance in beans (Phaseolus vulgaris L.) and their association with aboveground traits under water deficiency have not been quantified widely. Therefore, the effect of drought stress on the association of nodule performance traits with shoot performance traits was investigated using six common bean lines with contrasting differences in their adaptation to drought and low phosphorus (P) availability in soil. Drought stress reduced leaf water potential and gas-exchange characteristics (CO₂ assimilation, stomatal conductance) in all lines tested, but two drought-tolerant lines, BAT 477 and BT_34-1,-1, were superior in their ability to adjust their leaf water status under drought. These two lines were also superior in root growth, rate of CO₂ assimilation, vegetative biomass production, and nitrogen-fixing ability under drought stress. A direct relation of SNF and nodule fresh weight with gas-exchange traits and biomass production existed, suggesting that relative growth of shoot vs. root depends on the provision of nitrogen by SNF and photosynthetic carbon assimilation. Overall, differences found in nodule, root, and shoot performance traits indicated that the P-efficient bean line (BT_34-1-1) was superior to the other lines in adaptation to drought. Marked association of nodule performance traits with shoot performance traits under drought stress was detected. We suggest that nodule characteristics and SNF ability should be included with above- and below-ground traits as phenotypic markers in germplasm evaluation and breeding programs aimed at improving drought tolerance in common bean.