Construction of Drought-Resistant Microbial Consortium and Effect on Alfalfa Growth Under Drought Stress

Alfalfa (Medicago sativa L.) is an important perennial leguminous crop whose growth and yield are frequently limited by drought stress because the main planting areas are concentrated in arid and semi-arid regions. Plant growth-promoting rhizobacteria (PGPR) are crucial for enhancing plant stress resistance and constitute an attractive supplementary strategy for alfalfa production, but this has mainly been based on the use of single-strain inoculants in rhizobia. Here, we designed a microbial consortium to alleviate drought stress in alfalfa. Seven PGPR strains isolated from the rhizosphere and five rhizobial strains with in vitro growth-promoting properties obtained from alfalfa nodules were chosen. Based on a comprehensive evaluation of drought tolerance, growth-promoting traits, and metabolite-feeding experiments, we selected Sinorhizobium meliloti GAU-93 and Bacillus mycoides Y1 to construct a drought-resistant microbial consortium (DR-MC). A pot experiment indicated that inoculation with the microbial consortium enhanced drought resistance by increasing osmotic adjustment substance levels and reducing malondialdehyde content, promoting alfalfa growth. Separately, GAU-93 promoted aboveground growth by increasing photosynthetic pigment content under different water potential conditions, whereas Y1 enhanced root development and protected the plant from drought-induced oxidative damage. The DR-MC selected in this study is a valuable tool for further development to improve drought resistance in alfalfa.