Soils from different sunflower fields in West Azarbaejan province were collected, and then sunflower seeds planted in these soils. Forty five isolates of fluorescent pseudomonads isolated from rhizosphere of these plants through use of S1 medium. Pathogenicity test of these isolates on sclerotia demonstrated that 26 isolates exhibit antagonistic effects on sclerotia.The isolates B8,B29,and B38 caused highest incidence of non-viable sclerotia.Investigation on these rhizobacteria, in natural soil infected with fungus revealed that Benomyl, the isolates B119,B120,B111,and B112 provided the highest emergence of sunflower, respectively. Microscopic studies on the effects of fluorescent pseudomonads, on the fungus showed that hyphae secrete a large amount of cytoplasmic material that gathered and coagolated around hyphae. In this region abnormal hyphae such as coiling ,necrosis ,and ramificated hyphae were observed. Sixty eight percent of rhizobacteria, and also CHA0 produced hydrogen cyanide.Application of the isolates in vitro (dual culture),demonstrated that isolates CHA0,B112,B119,and B38 had the highest level of inhibition.Study on the volatile metabolites in isolates indicated that these isolates inhibited the growth of fungus. The isolates B112,and B120 inhibited growth of fungus near to 100 precent.Effect of isolates on increasing growth of sunflower showed that isolates B112,B119,and B111 had the most effect ,respectively. All bacteria, effective against the fungus were diagnosed as Pseudomonas fluorescens.
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