Improved salinity tolerance of Medicago sativa and soil enzyme activities by PGPR

Abstract Abiotic stresses such as salinity are common adverse conditions that significantly affect agricultural productivity worldwide. This study aimed to select halotolerant plant-growth-promoting rhizobacteria (PGPR) capable to promote plant growth and to improve soil functioning under salinity stress conditions. Thirty-two bacterial isolates were studied for their PGP traits and NaCl resistance. Four selected potential PGPR were identified by using 16S rDNA sequencing and tested for their PGP traits in the presence of 2–6% NaCl. Their effect on growth, chlorophyll content, oxidative stress and root arbuscular mycorrhizal (AM) colonization of Medicago sativa, was studied under salt stress in pots experiment. The bacteria were also tested for their effect on soil enzyme activities. Overall results showed that the isolates displayed various PGP properties and variable levels of NaCl resistance. The four selected potential PGPR strains were identified as Pseudomonas putida, Alcaligenes sp., Klebsiella sp., and Pseudomonas cedrina. The bacteria retained most of the PGP traits in the presence of the tested concentrations of NaCl. The inoculation of M. sativa plants by the four strains allowed overcoming the negative effects of stress due to NaCl and increased plant growth, roots AM colonization and the leaves chlorophyll content, compared to the non-inoculated control. It also lowered the levels of the indicators of oxidative damage, malondialdehyde, hydrogen peroxide, and proline. Besides, the strains had a positive effect on soil phosphatase, β-galactosidase, and arylamidase activities. This study showed that the selected isolates have an interesting potential to be used as bio-inoculants for plants growing under salt stress.