Impact of antibiosis in the rhizosphere on pathogenicity gene activation and biocontrol of bacterial-mediated solanaceous plant diseases

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An increased interest in biocontrol of plant pathogens has been fuelled by ineffective chemical control measures against certain diseases and public concern over the use of chemicals in the environment. It has been demonstrated that several rhizobacteria, such as Pseudomonas spp., can control plant pathogen populations under in vitro or controlled conditions using antibiosis, which involves the production of antimicrobial metabolites. However, the efficiency of antibiosis under soil conditions is still variable, explaining why only few antimicrobial metabolite-producing rhizobacterial strains have been commercialized. A better understanding of the microbial dynamics in the rhizosphere of plants and in situ action of antibiosis would favour large-scale use of Pseudomonas spp. for biocontrol. Solanaceous plant species, mainly potato and tomato, are important to the Canadian economy. These crops are attacked by numerous pathogens causing important economic losses. Here, I propose to study the impact of tailored antimicrobial metabolite producing Pseudomonas spp. inoculations on disease protection against two important bacterial plant pathogens affecting Solanaceae: Streptomyces scabies causing common scab of potato and Clavibacter michiganensis subsp. michiganensis causing bacterial wilt and canker of tomato. The general goal of this research is to understand, at the molecular level, how antibiosis operates in the rhizosphere, its effect on the colonization and infection of plants by bacterial pathogens, and the protection it offers against Solanaceous diseases. Specific goals are to: 1) Characterize the transcriptional activity associated with Pseudomonas spp. antimicrobial metabolite production in the rhizosphere of potato and tomato and its impact on controlling bacterial plant diseases. 2) Study the impact of rhizobacterial antimicrobial metabolite production on pathogenicity and virulence gene activation in S. scabies and C. m. michiganensis. Assessing if antimicrobial metabolite production can be sustained over time in the rhizosphere and determining if this can repress pathogenicity and virulence gene activation in pathogens represents an interesting avenue to control Solanaceous plant diseases.