Impact of bacterial consortium ratios on alfalfa growth and salt stress tolerance

The main purpose of this study is to elucidate the effect of bacterial ratio of different plant growth-promoting rhizobacteria (PGPR) consortia on alfalfa growth. The impact of the used ratios on physiological responses of alfalfa to salt stress was further assessed. Accordingly, two endophytic bacteria (SmA and RpB) were selected based on their halotolerance and plant growth-promoting properties, such as phosphate solubilization, biofilm formation, and phytohormones and exopolysaccharides production in response to salt stress when applied singly or in combination. The results showed that both single and mixed inocula significantly increased plant growth compared to non-inoculated treatments. Efficiency of inoculation was influenced by the strain species and the bacterial consortium ratio. The collected data further revealed that inoculation protects alfalfa plants from salt stress by preserving membrane stability and integrity from peroxidation, improving water status, protecting the photosynthetic apparatus, reducing the absorption of Cl^- ions and preserving K⁺/Na⁺ ratio. In fact, in the most tolerant plants, catalase activity was the most stimulated, in contrast to the most salt-sensitive species. This study clearly indicated that the consortium combining SmA and RpB at a 2/1 ratio outperforms the 1/1 and 1/2 ratios in removing the deleterious effects of salt stress, highlighting for the first time the importance of the ratio in the formulation of bacterial consortia.To validate the effectiveness of this biofertilizer in the field, further work is required, taking into account the combined impact of environmental factors such as soil and climatic conditions on alfalfa growth and development.

The online version contains supplementary material available at 10.1007/s13205-025-04654-2.