Screening of plant growth promoting rhizobacteria as potential microbial inoculants

Abstract Plant growth promoting bacteria can enhance and promote plant growth and development in different ways. These mechanisms include solubilization of phosphorus, nitrogen fixation and biocontrolling effects on phytopathogenic microorganisms. Suppression of phytopathogenic fungi by 47 different bacteria, isolated from different monocotyledonic plants rhizosphere and soil, was tested against Fusarium oxysporum radicis-lycopersici , Sclerotium bataticola , Pythium ultimum , Fusarium graminearum , and Alternaria spp. The antifungal activity of these isolates was described based on the comparison of the growth rate inhibition. As the production of iron-chelating compounds is one of the mechanisms responsible for the antimycotic effect, we tested the siderophore producing capacity of the isolated strains. Also, we assayed the ammonia production of these bacteria. This secondary metabolite compound contributes to the biocontrolling property of these bacteria. Our examinations also include the inorganic phosphate solubilization capacity of these isolates, which may improve the phosphorus uptake of plants. The results indicate that 17 bacterial isolates are able to produce siderophores and 30 from them possess capacity of calcium-phosphate mobilization. The majority of the cultures were found to have highly inhibitory effects against the mycelium growth of P. ultimum , F. oxysporum radicis-lycopersici and F. graminearum , whereas others showed little activity. Only twelve bacteria showed no activity against the S. bataticola plant pathogen fungus.