Inoculation with Azotobacter spp. Improves Eggplant Tolerance to Combined Salt and Drought Stress

Abstract This study evaluated the effects of a commercial rhizobacteria consortium on the growth and stress tolerance of eggplant seedlings under combined drought and salt stress conditions. A greenhouse experiment was conducted using a randomized plot design with five replicates. Eggplant seedlings inoculated with Azotobacter vinelandii and Azotobacter chroococum were exposed to drought (60% field capacity, FC), salt stress (50 mM NaCl), and their combination (60% FC + 50 mM NaCl). The inoculation alleviated the negative effects of combined stress on growth parameters, such as root development, shoot diameter, and shoot length. Inoculated plants exhibited improved stomatal conductance ( g s ), increased Ca in roots, enhanced accumulation of Ca, K, and Mg in leaves, and reduced Na accumulation in both roots and leaves. Malondialdehyde (MDA) levels decreased by 32%, alleviating oxidative stress. Increased proline (24%), total phenolics (22%), and anthocyanin (12%) contents in inoculated plants alleviated oxidative stress under combined stress. Enzyme activities of superoxide dismutase (23%), catalase (14%), and glutathione reductase (2%) were relatively insufficient to fully counteract the effects of combined stress in inoculated plants. The results showed that the commercial inoculum containing Azotobacter vinelandii and Azotobacter chroococum increased stress tolerance by significantly improving the growth and physiobiochemical properties of eggplant seedlings grown under the combined effects of drought and salinity stress.