Abstract
Abstract Two greenhouse studies were conducted to investigate the relationship between water stress and N2 fixation among drought-resistant and susceptible cowpea [Vigna unguiculata (L.) Walp.] genotypes. In both experiments, seeds were planted in 7.6-liter black polyethylene pots containing composted sawdust medium and were inoculated with Rhizobium. Throughout the experiments, flowers were removed to maintain vegetative growth. Water stress treatments were imposed by withholding water, while the control plants were watered as needed. The treatments were applied 58 and 56 days after planting (DAP) in the first and 2nd experiments, respectively. In both experiments, leaf water potential (LWP), shoot fresh weight (SFW), shoot dry weight (SDW), root fresh weight (RFW), nodule fresh weight (NW), nodule number (NN), and plant specific activity (PSA) by both in situ and destructive acetylene reduction methods were measured. Repeated observations of in situ acetylene reduction were made 58, 63, and 71 DAP in the first experiment. All other variables were measured 77 to 78 DAP in the first experiment. Single observations of all variables, including in situ and destructive acetylene reduction were made 56, 67, and 81 DAP in the 2nd experiment. Results suggested that resistant genotypes are capable of maintaining LWP and biomass production (as measured by SDW and SFW) during water stress. In addition, the effect of water stress on N2 fixation was far greater than the influence of genotype when genotypes were selected for relative drought resistance. Path analysis revealed that LWP is correlated to N2 fixation in water-stressed plants, and improvement of plant water status via drought resistance should increase N2 fixation potential under drought conditions. Therefore, breeding for drought resistance in conjunction with N2 fixation may be more beneficial than breeding strictly for N2 fixation potential without regard for environmental adaptation. The in situ method of acetylene reduction was found to be useful for detecting physiological changes due to water stress and estimating its genotypic N2 fixation potential.
Published Version
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