Evaluation of biocontrol characteristics of antagonistic bacteria isolated from cucumber rhizosphere against Sclerotinia sclerotiorum and Pythium aphanidermatum

Biological control of soil-borne diseases of plants has received serious attention among plant pathologists in recent years. In this regard, Rhizobacteria, more specifically fluorescent pseudomonads are known as an effective biocontrol of plant diseases. Pseudomonas spp. are promising agents to manage the disease caused by Sclerotinia sclerotiorum and Pythium aphanidermatum. In this study, we screened 81 bacterial isolates from cucumber rhizosphere for their antagonistic effects against the pathogens using dual culture method and investigating their ability to produce inhibiting volatile metabolites. Results indicated that isolates 19C, 21B, 24A, 33B, 33C, 38A, 42D, and 43C had significant inhibitory effects on the pathogens and their volatile metabolites significantly reduced the mycelial growth of the pathogens in comparison with controls. In greenhouse trials, isolates 19C and 24A reduced disease index of Pythium aphanidermatum more than 70% and that of Sclerotinia sclerotiorum more than 60% compared with controls. The isolates 19C, 24A, 33B, and 33C were able to produce protease. Isolate 19C was able to produce surfactin and isolates 33B and 33C were able to produce hydrogen cyanide. Molecular identification of isolates was conducted based on partial sequence of 16srDNA amplified by specific primers fD1 and rD1 thereby the isolates showed significant homology with Pseudomonas spp., Stenotrophomonas spp. and Flavobacterium spp.