Peer review

The aim of this study was to characterize fluorescent pseudomonads isolates of dryland wheat for salinity and drought tolerance and plant growth-promoting (PGP) traits in the presence or absence of salinity (4% NaCl) and evaluate the effect of two effective strains, Pseudomonas helmanticensis B30 and P. baetica B21, on phosphorus (P) uptake by wheat plant grown in a saline calcareous soil fertilized with rock phosphate (RP) and triple superphosphate (TSP) under water-deficit stress (55% of field capacity (FC) and 88% FC). All fluorescent pseudomonads isolates had the ability to grow at different drought stress levels and at salinity level of 4% NaCl. In addition, a significant percentage of these isolates retained their ability to produce PGP traits (especially P solubilization and indole-3-acetic acid production) in the presence of salinity. The results showed that 80% FC moisture level compared to 55% FC moisture level significantly increased plant growth indices and P uptake by wheat plant. In most of the measured parameters, RP treatment (8 mg P kg−1 soil) alone did not show any significant difference compared to negative control (without RP and TSP), but combination treatments with RP and TSP at all levels (3, 6, and 9 mg P kg−1 soil) increased these parameters compared to negative control. In non-stress and water-deficit stress conditions, bacterial strains significantly increased soil available P, growth indices (a 41.6% increase in root dry weight and an 11% increase in shoot dry weight), grain yield (a 17% increase), shoot P uptake of wheat plant as compared to control (without bacterial strains). Overall, the results of this study showed that dryland wheat rhizosphere harbors drought- and salinity-tolerant phosphate-solubilizing fluorescent pseudomonads isolates with potential of producing PGP traits in the presence or absence of salinity and improving P uptake by the plant under water-deficit stress.

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