Representatives of fluorescent pseudomonad strains were assessed for their antagonistic activity against the blackleg of potato pathogen, Pectobacterium carotovorum subsp. atrosepticum. Tested strains belonged mainly to Pseudomonas fluorescens Biovars III, IV and V and they could produce inhibition zone on PDA medium against P. c. subsp. atrosepticum ranging from 1.5-5.5cm. Six selected strains were used in two concentrations 10⁷-10⁹ and 10¹⁰-10¹² colony forming units to control potato blackleg disease caused by P. c. subsp. atrosepticum under greenhouse conditions. Results showed that all strains applied could reduce the disease ranging from 46 to 71 percent. There was no significant difference among strains and their two concentrations under greenhouse conditions. Most of the strains applied increased potato fresh weight and all of them produced antibiotic and siderophore compounds in vitro.

Keywords: Biological control, Blackleg, Pseudomonas fluorescens, potato, Pectobacterium, Iran.

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