Novel PGPR rhizobacteria from Artemisia and Salicornia rhizospheres alleviate the undesirable effects of salinity stress in tomato seedlings

• Seven bacteria isolates were identified as Pseudomonas sp., Paeniglutamicibacter sp., and Serratia sp. genera by sequencing the 16S rRNA gene. • In vitro screening showed the novel PGPR bacterial affect the plant growth-promoting traits from nutrient solubilization to biochemical production. • PGPRs inoculation of tomato seedlings appear to be a significant factor in altering their morphophysiological and biochemical processes under salinity stress. • The results confirmed that PGPR isolates can mitigated the undesirable effects of salinity stress on tomato seedlings. This study aimed to isolate and characterize salt-tolerant rhizobacteria from the rhizospheres of Artemisia and Salicornia and evaluate their potential to mitigate salinity stress in tomato seedlings under greenhouse conditions. Seven bacterial isolates of novel members of Pseudomonas sp., Paeniglutamicibacter sp., and Serratia sp. genera were identified by sequencing the 16S rRNA gene. High multiple bioactivities including enzymatic activity, biochemical secretion, phytohormone synthesis, and nutrient elements solubilizing in bacterial biomass validated by qualitative screening for rhizobacteria. Quantitative screening resulted that rhizobacteria exhibited a high tolerance to salt stress (102.5 mM NaCl) and consequently, prevented a decrease in bioactivity with increasing NaCl concentration, where isolates SHA, SHB, 3A, and 3B revealed maximum potential, respectively. These interesting results suggest that candidate isolates could be used as bioinoculants on model plants under salinity stress. As expected, salinity stress induced undesirable effects on growth of tomato seedlings. Duncan’s test indicated that rhizobacteria inoculation not only induced significantly ( p ≤ 0.05) the growth of tomato seedlings, but also preserved chlorophyll degradation, relative water content holding, and stomatal conductance facilities under salinity stress, depending on bacterial strain compared to non-inoculated tomatoes. Furthermore, bacterial inoculation significantly promoted a higher proline (73.42 mg g -1 FW) accumulation to mitigate the adverse effects of salinity stress and protected tomato seedlings from lipid peroxidation, as proved by a significantly reduced malondialdehyde level. Overall, the results of this study indicated that the salt-tolerant rhizobacteria have high potential for application as bioinoculants to enhance the production of horticultural crops under salinity stress conditions.