Evaluation of Biological Control Traits in Some Isolates of Fluorescent Pseudomonads and flavobacterium

Plant growth promoting rhizobacteria (PGPR) consisting a wide range of beneficial soil bacteria inhabiting rhizosphere of plant. Fluorescent pseudomondas are the most important plant growth promoting rhizosphere bacteria in different crop plants. In this research, twenty-five isolates of fluorescent pseudomonads isolated from forty soil samples of wheat rhizosphere and forty four isolates of Flavobacterium selected from the bacterial strains collection were employed. The ability of these isolates for production of chitinase, Salicylic acid, siderophore and hydrogen cyanide and antifungal activity against Rhizoctonia solani were determined. Results revealed that all the fluorescent pseudomonads isolates were able to produce siderophore on Chrome Azurol S (CAS) agar plates and siderophore is an important secondary metabolite in plant growth promotion and antifungal activity. In CAS agar method, the range of siderophore production was 0.34-1.21 halo diameter per colony diameter. None of these isolates were capable for chitinase production. Salicylic acid (SA) production by the isolates ranging from 0-10.91 g.ml-1 (average 2.48 g.ml-1). Bacterial ability for production of hydrogen cyanide had a great variation and based on this ability they were qualitatively classified in to high, relatively high, moderate and no production. Productions of studied metabolites were not detected in Flavobacterium isolates. Three isolates (PA24, PA1 and PA18) of fluorescent pseudomonads showed in vitro antifungal activity against Rhizoctonia solani. In contrast none of Flavobacterium isolates showed growth inhibition against the tested fungus. Results of this study showed that fluorescent pseudomonads which are native to soils of Iran had the potential to be used for promotion of plant growth and suppression of soil-borne plant pathogens. In contrast, Flavobacterium seem to be an inefficient rhizobacterium against plant pathogens because of incapability to production of some important secondary metabolites in plant growth promotion and antifungal activity. There is a need to study their effects on different agricultural crops.