Efficient rhizobacteria promote growth and alleviate NaCl-induced stress in the plant species Sulla carnosa

The present work aims to characterize native bacteria from the saline rhizosphere of Sulla carnosa and to identify promising rhizobacteria isolates able to ameliorate the salt tolerance of this species. Bacteria were screened in vitro for salt tolerance capacity and plant growth promoting characteristics (PGP). Selected NaCl-tolerant bacteria showing a high PGP potential were further characterized for plant promotion effects on the growth of S. carnosa under salt stress (200 mM NaCl). Three putative salt-tolerant strains that showed multiple PGP-traits identified as Acinetobacter sp. (Br3), Pseudomonas putida (Br18) and Curtobacterium sp. (Br20) were selected for inoculation study. In a greenhouse experiment, NaCl significantly disturbed physiological parameters in noninoculated S. carnosa. In these plants, NaCl reduced growth, increased foliar proline and malondialdehyde concomitant to Na-+/- shoot concentrations. However, bacterial inoculation with selected PGP isolates ameliorated significantly plant growth and alleviated salt-induced physiological disturbances. Hence, as compared to non-inoculated plants, inoculation provided a significant increase in dry biomass and increased photosynthetic efficiency and chlorophyll leaf content under saline condition. Additional analysis showed that microbial inoculation also enhanced total soluble sugars content and antioxidant enzymes activities thereby preventing reactive oxygen species (ROS)-induced oxidative damage in plants. These results suggest that the inoculation of NaCl-stressed plants with selected salt-tolerant PGPR inocula exert beneficial effects on plant growth by alleviating salt-induced toxicity stress on plant growth and development.