An Approach of Improving Plant Salt Tolerance of Lucerne (Medicago sativa) Grown Under Salt Stress: Use of Bio-inoculants

Abstract

This study was conducted to examine the effects of the combined application of rhizobial strains and plant growth-promoting rhizobacteria at different ratios on growth and salt tolerance of lucerne. Vegetative growth, relative water content, photosynthetic pigments and organic and inorganic solute contents in leaves were measured after 6 weeks of sowing. The results showed that bacterial inoculation significantly increased shoot and root dry weight, leaf number and relative water content whereas salinity reduced the growth of plants mainly in root dry weight and leaf area. However, the obtained results showed a significant improvement in the growth under salt stress of inoculated plants compared to non-inoculated ones. Regarding photosynthetic pigments, inoculation and salt induced significant variations in the total chlorophyll content, whereas changes in carotenoids remained insignificant. The inoculated plants accumulated less sodium and chloride and maintained a constant potassium content compared to non-inoculated plants. This would imply that the bacteria have retained Na+ and Cl− and so have consequently limited their translocation to the leaves and have promoted selectivity of K+ ions relative to Na+. The levels of organic solutes and soluble proteins were not significantly affected in most plants by both salt and bacterial inoculation, suggesting that they are not directly involved in the strategy of salt tolerance of Lucerne. These results indicate that inoculation with these plant growth promoting rhizobacteria could mitigate the adverse effects of soil salinity on growth of lucerne suggesting that these species could be used as bio-inoculants to increase productivity in arid and semi-arid lands.