Evaluation of plant-growth promotion and biocontrol characteristics in fluorescent pseudomonads isolated from vermicompost

Fluorescent pseudomonads are one of the most effective microorganisms among the plant growth-promoting bacteria. They have attracted many researchers attention due to their unique properties such as motility in the rhizosphere, high growth rate, and potential for the root colonization of various plants. In most studies, rhizospheric soils were used for isolation but Pseudomonas bacteria also have been isolated from various organic fertilizers. Therefore, the present study was conducted to evaluate plant-growth promotion and biocontrol characteristics of fluorescent pseudomonads isolated from vermicompost. Then, the ability of isolates was evaluated for auxin and siderophore production, tricalcium phosphate dissolution, and secretion of growth inhibitor metabolites. Total of 43 fluorescent pseudomonads isolates were isolated and purified based on irradiation under a UV lamp and fluorescence properties. Results of the PGP characteristics revealed that all the isolates were able to produce auxin and solubilize inorganic phosphorous. The average of auxin production was 2.51 mg/l. The highest (708 mg/l) and lowest (203 mg/l) amount of soluble phosphate belonged to P15 and P43 isolates, respectively. P35 isolate showed the most efficient in terms of siderophore production in which the ratio of halo zone diameter: colony diameter was 2.04 mm (after 48 hours) and 2.12 mm (after 72 hours). The results of the hydrogen cyanide production test showed that 88.35% of isolates could secrete this metabolite. In this research, all isolates were not able to produce protease enzymes. In terms of production of this enzyme, the P17 isolate showed the highest ratio of halo zone diameter: colony diameter (2.7 mm), was the most efficient one. None of the isolates were able to produce cellulase enzymes.