Book Description

Abstract: For centuries plant pathologists have been investigating the interactions of microbes and plants and have come to understand many of the strategies that microorganisms have developed for niche adaptation, host range specificity, nutrient acquisition and utilization and mechanisms of pathogenicity. Using this broad knowledge base plant pathologists have, unbeknownst to most consumers and many producers, developed economically feasible and environmentally sustainable management strategies that have protected our crops from devastating diseases such as wheat stem rust, late blight of potato, bacterial wilt of tomato, papaya ring spot and most recently soybean rust. Research in plant pathology addresses issues of food security with a focus on fundamental research, teaching and extension outreach. Traditionally research has focused on crop protection with respect to plant pathogens and toxins. However, the occurrence of multiple foodborne outbreaks on fresh produce over the last 10 years has broadened the scope of plant pathology research to include food safety issues related to fresh produce. Various sources and kinds of risk factors can be associated with the contamination of fresh produce by both plant and foodborne pathogens, and all must be managed adequately such that diseases are minimized and no harm comes to the consumer. Crop production practices significantly influence the quality and safety of fresh produce. For the research presented in this dissertation a systematic approach was used to assess pre-harvest and post-harvest microbial risks and management strategies used by vegetable farmers in the Midwestern United States and Kentucky. A survey-based confirmatory assessment of Midwestern vegetable producers' perspectives and practices regarding fresh produce safety hazards showed that although the majority of vegetable producers considered themselves familiar with national Good Agricultural Practices (GAPs) and agreed that implementing GAPs could reduce the risk of produce contamination, they were not consistently practicing GAPs. Producers' acknowledged that irrigation and run-off water, worker hygiene, raw and composted animal manure, wildlife droppings, field proximity to livestock or wildlife habitats, plant diseases and insects were potential sources of pre-harvest microbial contamination of produce, but paradoxically, disagreed that contamination most frequently originated on-farm. Vegetable producers preferred in-person modes of communication over mass media, factsheets or electronic modes, with only 17% having a preference for Internet or email based information. In a second survey-based study, the GAPs and integrated pest management (IPM) strategies used by vegetable growers were identified and the impact that these practices had on the microbial quality and safety of fresh produce was assessed. Although few differences in produce quality amongst management strategies used to produce leafy greens and tomato or peppers were identified the contamination of fresh produce with plant pathogens was identified as a risk factor for contamination of fresh produce with foodborne pathogens. In addition, fungicide treatments commonly used to manage plant fungal pathogens reduced the microbial quality of fresh produce. Cross-contamination of water used for agricultural purposes was also identified as an important risk factor. The majority of vegetable producers identified economic factors, management of wildlife intrusion and lack of knowledge and/or experience with GAPs as the main barriers to adopting GAPs. Plant and human pathogens contaminating surface water used for irrigation have the potential to significantly reduce yield and lower the microbial quality of vegetable produce, respectively. In combination with baiting and Phytophthora capsici-specific PCR, P. capsici was detected in five different sources of surface water used for routine irrigation of pepper and cucurbit crops in Ohio. This research represents the first report of P. capsici detection in surface waters used for irrigation in Ohio. Under field conditions, chlorine dioxide and chlorine gas injected into surface waters prior to rapid sand filtration was ineffective in reducing levels of P. capsici and variable in reducing fecal indicator microorganisms. The design and operational practices of treatment infection systems for management of plant and human pathogens in irrigation water need to be optimized before vegetable growers in Ohio invest any further time and money into these systems. A model for a multiple barrier approach to treating surface water for irrigation is described. The primary method to reduce spoilage and foodborne pathogens on produce is adherence to management strategies that prevent contamination, however post-harvest disinfection remains a critical step in the production of high microbial quality, safe produce. The microbial quality of fresh cut and whole head lettuce, whole tomatoes and detached grapes after exposure to micro-droplets of the sanitizing agents StorOx (hydrogen dioxide) or KleenGrow (quaternary ammonium) produced using de-correlation humidification technology was evaluated in this research. High concentrations of both disinfectants eradicated Salmonella enterica Serovar Typhimurium on whole tomatoes but not E. coli O157 populations on whole or cut heads of lettuce. Coliform and lactobacilli, E. coli and yeast and molds were not detected on non-treated grapes and aerobic bacteria were less than or equal to Log10 2.7. Populations of aerobic and lactobacilli bacteria were significantly higher on grapes exposed for 10 sec to 1% and 4% StorOx than the non-treated controls, but were not higher after a 30 sec exposure time at the same concentration.