Fereshteh Bayat

Damping-off disease caused by Pythium spp. is one of the most devastating diseases of cucurbitaceae family, especially cucumber. Fluorescent Pseudomonads are able to control plant pathogens through producing different metabolites including antibiotics, siderophore, hydrogen cyanide and extracellular enzymes. In this study polymerase chain reaction (PCR) using B2BF and BPR4 primers were performed to monitor isolates harboring phlD gene, the key gene in biosynthesis of DAPG antibiotic. Results revealed that 8 strains had the target gene. Superior strains were selected based on preventing hyphal growth of Pythium ultimum through dual culture method on KB and PDA, that PGU1, PGU8, PGU7 and PGU6 isolates had highest antagonism capable against P. ultimum. The studied bacterial isolates were capable to produce siderophore, hydrogen cyanid, protease and inorganic phosphate solubilization ability. The ability of 4 selected bacterial isolates on biocontrol of pythium damping-off of cucumber in greenhouse was tested. Results showed that in control treatment (infected by P. ultimum but no bacteria inoculation) all seedlings died after 4 days, while treatments with bacteria isolates inoculation revealed various degree of disease control. It can be concluded that metabolite production and phosphate solublization capability of fluorescent Pseudomonads can make them effective biocontrol agents against soil borne pathogens as well as plant growth promoting microorganisms.