Population dynamics of bacteria including antifungal species in the rhizosphere of oilseed rape during its life cycle

Abstract

The population dynamics of different bacterial groups with antifungal properties was investigated in comparison with total bacteria based on colony forming units for successful biological control of the soil‐borne pathogen Verticillium dahliae var. longisporum Stark causing tracheomycosis of oilseed rape. This is the first report about bacterial population densities of a plant with a winter annual life cycle. Population densities of colony forming bacteria of oilseed rape (Brassica napus spp. oleifera Metzg. Sinsk.) were significantly lower in autumn and winter than in spring and summer. The number of antifungal bacterial populations like fluorescent pseudomonads, Bacillus spec. (spores) and Stenotrophomonas maltophilia also increased during life cycle. The percentages of antifungal isolates were 7 % on average and relatively stable during time of investigation as estimated by a bioassay in vitro. The antifungal mechanisms of 10 different isolates of each selected taxonomic group were investigated. The mechanisms were specific for each isolate. All of these selected strains showed antifungal activity against V. dahliae var. longisporum in vitro and therefore, they were evaluated as potential biocontrol agents against this pathogen.