The present study was designed to isolate and characterize plant growth promoting rhizobacteria (PGPR) from different Egyptian salt-affected soils and to evaluate the in vitro bacterial mechanisms related to plant growth promotion and their tolerance for sea water and sodium chloride added in culture media. Two hundred and seven isolates of bacteria and actinobacteria were isolated from salt-affected soils of different Egyptian governorates namely, Kafr El-Shikh (Sakha), El-Qalubia (Meet Kenana), El-Behira (El-Nubaria) and Port Said (Sahl El-Teina). Obtained data showed that the two more potent isolates in nitrogenase activity were identified as Azospirillum lipoferum D178 and Azospirillum lipoferum D207, while the isolates which gave high production of indole acetic acid were identified as Paenibacillus alive D135 and Bacillus pumilus D139, while the isolates which appeared highly inorganic phosphate solubilization were identified as Pseudomonas fluorescence D23 and Bacillus megaterium D159. The six identified strains were taken to examine their tolerance against different concentrations of sodium chloride (1-5%) and different dilutions of sea water (1:2 to 1:10 v/v). All strains under saline stress were able to produce indole acetic acid, gibberellines, catecolate-type siderophores and citric acid-type siderophores as well as their ability to solubilize inorganic phosphates. All the PGPR activities in the supplemented medium with NaCl or sea water were indicative of their tolerance to the salt. A decrease in activities values has been reported with increasing salt concentration. |
