Biocontrol of bacterial canker/wilt of tomato (Lycopersicum esculentum) caused by Clavibacter michiganensis subsp. michiganensis with rhizobacteria

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Clavibacter michiganensis subsp. michiganensis (Cmm) is the causal agent of bacterial wilt and canker of tomato (Lycopersicon esculentum), causing substantial economic losses worldwide. During the last decade research work on Cmm of tomato has largely focused on epidemiology, however, there has been little research on biological control. There is growing interest in organic production of tomatoes and biocontrol is compatible with this approach. The goal of this proposal is to screen plant rhizospheres for bacteria antagonistic to Cmm, and to investigate their ability to protect tomato plants against Cmm. We propose to isolate root epiphytic and endophytic bacteria from rhizosphere soil and plant root samples. These isolates will then be screened for activity against Cmm. A first small effort in this regard discovered four strains that show anti-Cmm activity, however, a wide range of strains must be identified as some are certain to be found unsuitable for commercial biocontrol, due to an application and product constraints, and to regulatory restrictions; a large number at the outset is the best strategy. The active strains will be analyzed for production of anti-bacterial compounds using HPLC, GC/MS and MALDI-TOF and/or NMR spectroscopy. The anti-Cmm activity of these compounds will be assessed via the disk diffusion assay (on agar plates), and the minimum inhibitory concentration of each will be determined. We will also study the anti-Cmm activity of combinations of biocontrol bacteria and their anti-Cmm compounds. In addition, we will study the tripartite association of the biocontrol strains/anti-Cmm compounds, Cmm and the host tomato plant. Greenhouse studies will be conducted to study application sites (seed, root, foliar and various combinations of these) for biocontrol bacteria and their antibiotics in a range of combinations, for the control of Cmm. We will also determine if these bacteria/anti-Cmm compounds are able to induce disease resistance in tomato plants, thus adding to host plant defense activity against the pathogen. Finally, studies on the control of Cmm by biocontrol strains/anti-Cmm compounds will be conducted under conditions similar to commercial greenhouses.