Isolation and Screening of Inorganic Phosphate Solubilizing Pseudomonas Strains from the Lotus creticus Rhizosphere Soil from the Northwest of Morocco

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In vitro screening of plant growth-promoting (PGP) traits was carried out using 63 Pseudomonas, isolated from the rhizosphere of Lotus creticus collected from the northwest region of Morocco. The isolates were tested for their capacity of solubilizing tricalcium phosphate (TCP) on Pikovskaya (PVK) solid medium, and 20 Pseudomonas could solubilize TCP. We then selected five phosphate solubilizing bacteria (PSB) based on their halo diameters to undergo more tests. As a result, all five isolates were positive for hydrogen cyanide (HCN) production, and the amount of indole acetic acid (IAA) produced by them fluctuated between 5.72 ± 0.09 mg/L and 195.16 ± 0.38 mg/L. All the selected strains could produce siderophores. Except urease activity, all isolates possessed at least two enzyme activities such as cellulase, chitinase, protease, and amylase activities. In addition, all these PSB were able to produce ammonia. Thus, the strains were evaluated by TCP solubilizing quantitative assay in PVK liquid medium. The concentrations of solubilized P were between 20.80 mg/L and 159.55 mg/L. This solubilization was accompanied by a pH decrease of the medium from 7 to 4.16. Furthermore, the five PSB were tested in vitro for antagonism against phytopathogenic fungus Fusarium oxysporum, and all the PSB except LCP18 strain were capable of inhibiting its growth.