Molecular characterization of bacterial antibiosis in the rhizosphere and its impact on Solanaceous plant diseases

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An increased interest in biocontrol of plant pathogens has been fuelled by public concern over the use of chemical pesticides in the environment and ineffective chemical control measures against certain diseases. It has been demonstrated that several antagonistic Pseudomonas spp. can control plant pathogen populations under in vitro or controlled conditions using antibiosis. However, the efficiency of antibiosis in soil is still variable, explaining why only few antimicrobial metabolite-producing Pseudomonas spp. strains have been commercialized as biopesticides. Here, it is proposed that two Solanaceous plant species, potato and tomato, be used to study the effect of tailored antimicrobial metabolite-producing Pseudomonas spp. inoculations against two important bacterial plant pathogens: Streptomyces scabiei (Ss) causing common scab of potato and Clavibacter michiganensis subsp. michiganensis (Cmm) 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, how it affects the transcriptomics of Ss and Cmm, its effect on colonization and infection of plants by pathogens, and how it can protect against diseases. A collection of Pseudomonas spp. producing antimicrobial metabolites such as phenazine-1-carboxylic acid (PCA), 2,4-diacetylphloroglucinol (DAPG) and hydrogen cyanide (HCN) has been isolated in our laboratory. Knockouts of these strains, incapable of producing the antimicrobial metabolites, have also been developed. These organisms will be used to address the following specific goals: 1) Characterize the transcriptional activity associated with Pseudomonas spp. antimicrobial metabolite production in the rhizosphere of potato and tomato and its impact on controlling plant diseases. 2) Study the impact of antimicrobial metabolite production on Ss and Cmm transcriptomics. 3) Determine if antimicrobial metabolite production can, in addition to antibiosis, trigger induced systemic resistance (ISR) in Solanaceae. This innovative work should lead to a better understanding of how Pseudomonas spp.-mediated antibiosis operates under soil conditions and how it can contribute to disease protection in Solanaceae.