Pseudomonas fluorescens DR54 reduces sclerotia formation, biomass development, and disease incidence of Rhizoctonia solani causing damping-off in sugar beet

Effects of the biocontrol strain, Pseudomonas fluorescens DR54, on growth a nd disease development by Rhizoctonia solani causing damping-off in sugar b eet were studied in soil microcosms and in pot experiments with natural, cl ay-type soil. In pot experiments with P. uorescens DR54-treated seeds, sign ificantly fewer Rhizoctonia-challenged seedlings showed damping-off symptom s than when not inoculated with the biocontrot agent. In the rhizosphere of P. fluorescens DR54 inoculated seeds, the bacterial inoculant was present in high numbers as shown by dilution plating and immunoblotting. By the ELI SA antibody technique and direct microscopy of the fungal pathogen grown in soil microcosms, it was shown that the presence of P. fluorescens DR54 on the inoculated seeds had a strong inhibitory effect on development of both mycelium biomass and sclerotia formation by R. solani. In the field experim ent, plant emergence was increased by treatment with P. fluorescens DR54 an d the inoculant was found to be the dominating rhizosphere colonizing pseud omonad immediately after seedling emergence.