Abstract

The use of biological approaches instead of chemicals to improve agricultural production has captured the interest of agronomists for a long time. With the aim to select beneficial bacteria exhibiting several plant growth promoting (PGP) traits, 44 bacteria were isolated from the rhizosphere of the legume Lupinus hirsutus L., and tested for solubilization of tricalcium phosphate (Ca3 (PO4)2). Of 35 phosphate solubilizing rhizobacteria, 14 isolates were selected for their solubilization diameters (0.6-1cm). Four bacteria were able to produce indole acetic acid (IAA), while none was positive for hydrocyanic acid (HCN). Other PGP traits (siderophores production, Atmospheric nitrogen fixation and ACC deaminase) were searched for these 4 bacteria. Except the isolate RL5 strain which showed ACC deaminase activity, all strains were unable to produce siderophores or to fixe nitrogen. Phosphorus solubilizing ability of these 4 strains was tested in liquid medium with 0.5% Ca3(PO4)2, and the values of soluble P were ranged between 81.94 and 298.66 mg / l after 7 days of incubation, obtained respectively by RL77 and RL10. This bacterial solubilization of P was accompanied by a fall in pH to pH 4.83 in presence of RL10. These isolates were shown to belong to the genus Enterobacter. The rice inoculation test (Puntal variety) was performed in pots substituting soluble P by Ca3 (PO4)2. Significant increases were obtained for shoot length and dry weight of plants in presence of RL5, RL10 and RL16, as compared to the control. However, RL77 showed a significant decrease of the different parameters.