detection of hcnab and phld genes in fluorescent pseudomonads biological control agent of fusarium graminearum and studying their ability to ectorhizosphere colonization of wheat

the biological control ability of fluorescent pseudomonas spp. results from competition for space and untrient, antibiosis and colonization in the rhizosphere. biocontrol fluorescent pseudomonads produce a wide variety of antibiotics. in this study, the biocontrol ability of 39 strains of biocontrol pseudomonas fluorescens, was examined against fusarium graminearum the causal agent of wheat fusarium head blight in vitro. growth inhibition of f. graminearum was examined by a dual culture test and the antifungal activity of bacterial volatile and nonvolatile metabolites. in all experiments, four strains of pseudomonas fluorescens p13, utpf127, utpf125 and utpf105 were the most effective in controlling the pathogen. these strains were evaluated for screening the phld and hcnab genes and their ability to colonize ectorhizosphere of wheat under greenhouse conditions in 14, 28 and 42 days after planting. hcnab gene was detected in all strains while phld was detected in all bacteria except for p13. wheat seeds were inoculated with the same concentration (108 cfu/ml) of each strains and sterile distilled water as a control and bacterial populations were enumerated on selective kb+++ medium. the results showed that there are significant differences among strains in different days. bacterial population colonizing the ectorhizosphere was decreased by the time. p13 and utpf125 strains couldn’t be detected in 42nd day, on the other hand, they could be detected in 28th days more than 1.8×104 cfu/g (fresh weight of root). utpf127 population remained in ectorhizosphere at 1.1×104 cfu/g (fresh weight of root) in 48th day.