Co-Inoculation of Common Bean with Rhizobium and Azospirillum Enhance the Drought Tolerance

Plant growth-promoting rhizobacteria (PGPR) have been shown to reduce the negative effects of drought on numerous plant species, but these effects are unknown for common bean ( Phaseolus vulgaris L.) crop. The study aimed to investigate the effects of inoculation with Rhizobium tropici , Azospirillum brasilense and the co-inoculation with both rhizobacteria on the nodulation, growth and tolerance of common bean plants to drought stress. Three water replenishment regimes [100% of pot capacity (non-stress control), 50% of pot capacity (moderate stress) and 25% of pot capacity (severe stress)] and four seed inoculation treatments: control (non-inoculated), inoculation with R. tropici , inoculation with A. brasilense ; and co-inoculation with R. tropici and A. brasilense were studied in an experiment arranged in a 3 × 4 factorial scheme with four replicates. Relative water content (RWC), membrane stability index, nodulation, relative chlorophyll index, plant growth, and grain production were recorded. The inoculation of common bean plants with R. tropici and A. brasilense , and the co-inoculation improved leaf membrane stability and minimized the water loss from leaf tissue of plants under water stress conditions. Plants co-inoculated with R. tropici and A. brasilense had greater nodulation and relative chlorophyll index under severe drought stress. The inoculation with A. brasilense and the co-inoculation can attenuate the pod abortion rate of bean plants under moderate drought conditions but had no effect under severe stress conditions. Co-inoculation of A. brasilense and R. tropici alleviate the negative effects of water stress and maintain growth and grain yield of the common bean plants, and therefore, this management practice can be used by common bean farmers to enhance the plant tolerance to drought.