Bradyrhizobium brasilense Strains from the Brazilian Semiarid Region Modulate Soybean Responses to Drought Under Greenhouse Conditions

Abstract Soybean cultivation in semi-arid regions is challenging, and the search for strategies to mitigate the effects of drought caused by prolonged dry spells has increased each year. The objective of this study was to evaluate the efficiency of three strains of Bradyrhizobium brasilense , native to the Brazilian semi-arid region, in alleviating drought-induced damage in soybean. The study was conducted in a greenhouse using a randomized block design and a double factorial scheme (6 × 2), consisting of six nitrogen (N) sources [inoculation with UFLA 06–19, UFLA 06–21, UFLA 06–22, a commercial inoculant, and two uninoculated controls (one with mineral N and the other without N application)] and two water regimes [control at 60% of field capacity (FC) and drought at 45% of FC]. Drought negatively affected physiological parameters (stomatal conductance, internal CO₂ concentration, net photosynthesis, and instantaneous water use efficiency), growth (morphometric parameters and biomass production), and nitrogen accumulation in plants. However, stress damage was less severe in plants inoculated with B. brasilense strains or supplied with mineral N compared with plants inoculated with the commercial inoculant. Under drought, plants inoculated with B. brasilense exhibited increases in instantaneous water use efficiency, leaf area, nitrate reductase, guaiacol peroxidase, and superoxide dismutase activities, as well as greater nitrogen accumulation relative to the other treatments. These results highlight the suitability of strains UFLA 06–19, UFLA 06–21, and UFLA 06–22 for use as inoculants in soybean cultivation in semi-arid regions.