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A Systems Approach to Managing Microbial Threats to Greenhouse Tomatoes


The long-term goal of this project is to significantly increase the competitiveness, profitability, safety and sustainability of the greenhouse tomato industry by elucidating the critical points of introduction and spread of high-risk plant and human pathogens, providing new widely accessible prevention and mitigation tools and approaches, and applying these tools and approaches to manage microbial threats. The approach relies on intensive interaction between researchers and growers to develop realistic, science-based Best Management Practices (BMPs) compatible with greenhouse tomato food safety GAPs. Specific objectives are: <OL> <LI>Develop a system-wide framework in which the introduction and spread of plant and human pathogens in greenhouse tomatoes can be effectively managed; <LI>Develop diagnostic technologies for accurate, rapid and cost-effective pathogen detection;<LI> Understand the etiology and factors affecting the epidemiology of high-risk tomato pathogens; <LI>Develop approaches and technology suited to integrated management of high-risk plant and human pathogens;<LI> Assess the economic feasibility of technology and management strategies, incorporate appropriate technologies into Best Management Practices, and transfer BMPs to greenhouse tomato growers and assess their adoption.</OL> Expected Outputs <OL> <LI>A systematic framework to identify key plant and human pathogens and the points in the production flow in which they can be prevented or controlled. <LI> Best Management Practices (BMPs) for disease control in tomatoes. <LI>New, improved diagnostic assays to detect and monitor critical tomato pathogens. <LI> A better understanding of the etiology and factors affecting the epidemiology of tomato chlorotic stunting disorder and bacterial canker. <LI>Knowledge of the efficacy of different disinfectants in preventing mechanically transmitted diseases. <LI> A novel high throughput screen to identify Cmm- and Salmonella-inhibiting compounds from small molecule libraries, and promote promising material for further development. <LI>Near-term knowledge on the efficacy of disease management products for bacterial canker and Botrytis grey mold management. <LI>Completed survey of tomato greenhouse industry and affiliated professionals. <LI>Evaluation plan and evaluation tools for each product/program described above. <LI> Presentations and workshops delivered annually at existing industry educational programs. <LI> A series of workshops/webinars for educators and growers to aid in understanding individual grower risks and key control points in production as well as implementing solutions and control measures. <LI>Annual roundtable discussions with key stakeholders. <LI> A comprehensive image library of greenhouse tomato diseases. 14. Fact sheets and technical bulletins, concise color identification flip charts, etc. for greenhouse tomato growers and educators. 15. Popular press articles on disease management products. 16. In-service training of extension educators.

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Non-Technical Summary: Nearly 40% of tomatoes sold in U.S. grocery stores are produced in greenhouses, and are valued for high quality and year-round availability. The greenhouse tomato industry identified disease management as its most serious production problem and better, more cost-effective disease management practices as its highest priority need. Their identified priority diseases are bacterial canker, viroids, Pepino mosaic virus and Botrytis gray mold. Further, foodborne human pathogens pose a significant risk to the industry at large. The industry's aspiration and the goal of this project is to increase the sustainability of greenhouse tomato production by improving food safety and disease management approaches. This Standard Research and Extension Project addresses critical disease management and food safety issues in the greenhouse tomato industry. This systems-based, trans-disciplinary project aims to design Best Management Practices (BMPs) and develop tools that will improve the efficiency, profitability, safety and economic competitiveness of the greenhouse tomato industry. The systems approach considers all phases of tomato production from seeding through propagation, production and harvest. It identifies key problems/obstacles, sets priorities, develops solutions, assesses the economic impact of solutions, and provides outreach to a broad community of greenhouse tomato growers. The project adapts appropriate elements of the Hazard Analysis Critical Control Point system used to prevent contamination in food processing to aid prevention and control of microbial threats in greenhouse tomato production. We will develop model production flow diagrams, assess risks, identify pathogens, and identify critical control points for pathogenic risk where control efforts should be focused. Tools and methodologies to aid design and insure the efficacy of BMPs, include disease diagnostic assays, hygiene practices, crop protection materials, and guidelines for their use. The project is advised by greenhouse producers of all scales and proceeds in iterations that allow ongoing technical and user-acceptance assessment aiming to create a more biologically efficient and economically sustainable industry. Large-, medium- and small-scale greenhouse tomato producers will benefit from the outputs of this project through increased awareness of tomato-associated human and plant pathogens, critical points of pathogen entry and subsequent contamination of greenhouse operations and approaches to disease management, as well as access to new technology. Reducing quantity and quality losses at all scales has immediate economic impact on both producers and consumers of greenhouse tomatoes. Technologies developed by this project create and extend capacity in allied support industries for growers. This project also improves and enhances the use of biorational chemicals in the greenhouse industry, which has both positive economic and environmental impacts. Efforts to prevent illnesses associated with fresh produce benefit society at large by encouraging confidence in produce safety and consumption of healthful products. <P> Approach: A mail survey targeting 500 growers will be conducted in Year 1, with a follow-up in Year 4 to assess adoption/change in knowledge. Operational Risk Management analysis will be done according to industry standards. Critical control points will be identified at different flow points at each of 8-10 operations. Existing monoclonal antibodies and new molecular technology will be used for on-site detection assays and robust fingerprinting of populations of the bacterial canker pathogen. A real-time RT-PCR for a broad-spectrum detection of tomato viroids will be developed. A virus-viroid surveillance system will be developed to identify critical control points in greenhouse tomato operations. The influence of humidity, temperature and inoculum on Cmm infection and transmission during crop work will be studied using bioluminescent strain BL-Cmm17. Colonization will be determined nondestructively for 4 weeks by an in vitro imaging system (IVIS) and results confirmed by culturing at termination. Pathogenicity of TCDVd strains will be determined through mechanical inoculation of indicator plants. PCR amplicons will be sequenced and their phylogenetic relationships determined. The synergy between TCDVd and the endemic PepMV will be investigated by single and co-inoculation of tomatoes. Efficacy of disinfectants against plant pathogens will be evaluated in vitro, then by simulating crop work practices using a disinfected cutting tool. Their efficacy against Salmonellae will be evaluated in vitro, and promising materials will be tested using a produce fogger system on fresh tomato fruit exposed to Salmonella serovars by spot inoculation. A library of >50,000 small molecules will be screened for antimicrobial activity against BL-Cmm17 and bioluminescent Salmonella Typhimurium using a bacterial growth-inhibition assay. The five most promising inhibitors will be tested on > 200 Cmm or 25 Salmonella strains. Effective compounds will be tested for activity in larger plants (Cmm) or a fogging system (Salmonellae). Crop protectants will be evaluated alone or in combination for the control of bacterial canker or Botrytis gray mold according to standard protocols. All products will be applied as a foliar spray or through chemigation at rates suggested by the manufacturer, prior to inoculation, with additional applications as recommended. Data on costs of capital, labor, and materials in greenhouse tomato production will be collected using survey, case studies, and expert informant interviews and live process analysis. Production budgets for greenhouse tomato enterprises will be modified relevant to the impact of the project's outcomes. A decision model exercise will be developed for growers to decide whether and at what level to adopt project recommendations and technology outcomes. Annual meetings of the project team will include review and evaluation of progress to date and expert debate on implication of discoveries to the industry. Outreach efforts will each have an evaluation component to assess impact and inform future research and education needs.

Miller, Sally
Ohio State University
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