Abstract:
The effect of drought stress on the association of nodule performance traits with shoot
performance traits was studied 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 between symbiotic nitrogen
fixation and nodule fresh weight with gas exchange traits as well as biomass production
existed suggesting that relative growth of shoot vs. root depends on the provision of nitrogen
by symbiotic nitrogen fixation 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 than the other lines in terms of adaptation to drought. Results
showed marked association of nodule performance traits with shoot performance traits under
drought stress. 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 that are aiming for improving drought tolerance in common bean.
