Bacterial consortium based on Pseudomonas fluorescens, Lysinibacillus xylanilyticus and Bacillus velezensis reduces clubroot disease in broccoli

Abstract

Clubroot disease caused by Plasmodiophora brassicae is the most devastating disease in Brassicaceae plants. Control of clubroot is limited because of the survival of resting spores of the pathogen in the soil for years. Crop rotation, liming of the soil, fungicides and resistant cultivars have not been totally efficient in reducing the damages of the disease or pathogen spread. Although biocontrol with microorganisms has shown potential against clubroot, the variable results when using individual strains have made implementation difficult. Thus, the aim of this work was to determine whether a consortium of selected beneficial microorganisms is more efficient in controlling clubroot in broccoli than single strains. Single strains of bacteria from the Lysinibacillus, Bacillus and Pseudomonas genera (5 × 107 cells ml−1) and Trichoderma spp. (1 × 106 conidia ml−1) were evaluated in an initial screening. Four strains showing the best performance on plant growth and reduction of clubroot were evaluated as consortia in a further experiment. Treatments were applied in nursery (4 ml plant−1), and to the soil one week before transplant and the day of transplant (60 ml plant−1 each time). Plant shoot and root dry weight and the incidence and severity of clubroot were recorded. Supernatant from liquid cultures of Pseudomonas migulae Pf014 and Lysinibacillus xylanilyticus Br042, and washed cells of Bacillus velezensis Bs006 and B. pumilus Br019 promoted shoot growth of the plants. Single applications of Trichoderma asperellum Th034, Bs006, Br042 and Pseudomonas fluorescens Ps006 showed biocontrol potential against clubroot. However, the consortia built of Bs006, Br042 and Ps006 showed the highest reduction of clubroot incidence (78%) and severity (74%). A synergistic interaction by this consortium was found compared with the efficacy of single strains. To our knowledge, this work reports for the first time a consortium based on three rhizobacteria with high potential to control clubroot disease.