ABSTRACT
Rising soil salinity has been a major worldwide problem. This study was conducted to obtain Azotobacter cultures which can grow and produce plant growth promoting (PGP) activities under saline conditions with promising potential, as a bioinoculant for plants. The highly efficient isolate (19A) was selected from a total of twenty two rhizo bacterial isolates obtained from different geographic regions of salt affected soil in Egypt under NaCl concentration up to 5%. In vitro, the selected isolate recorded the highest nitrogenase activity, IAA production and gibberellins production at 1% NaCl concentration compared to other isolates. This isolate has been identified according to 16S-rRNA partial sequence analysis as Azotobacter salinestris strain NBRC 102611 and we have deposited it in Gene Bank under Accession No. (KU97890). Azotobacter salinestris was positive for amplification of nifH gene. Furthermore, it produced osmoprotectant substances as1aminocyclopropane-1- carboxylate (ACC) deaminase enzyme, Salicylic acid (SA), proline and exopolysaccharide (EPS). The results of sorghum inoculation with Azotobacter salinestris showed significant differences in all of vegetative growth parameters, photosynthetic pigments, macro-elements content, total carbohydrate and proline content as compared with control