Validating forensic tools for crop biosecurity: Case study investigation of salmon blotch of onions in Israel
Abstract
Globalization of agricultural commerce increases the vulnerability of the United States to introductions of plant pathogens by inadvertent or intentional means. Plant pathogen forensics combines traditional plant pathology and microbial forensics to enhance crop biosecurity. This research was designed to test and validate microbial forensic tools for plant pathogens in laboratory and field settings. A real-time PCR assay developed by the National Bioforensic Analysis Center for high consequence human pathogens was adapted and validated for the phytopathogenic bacterium, Xylella fastidiosa, which affects many plant species. PCR primers amplified genomic DNA from multiple strains of the bacterium and did not amplify near-neighbor microorganisms or animal or plant DNA. Other forensic tools were developed to investigate an actual outbreak, in Israel, of salmon blotch disease of onions, caused by the phytopathogenic fungus Fusarium proliferatum. A decision tool designed to assist first responders recognize signs of criminal activity at the field was implemented and a DNA fingerprinting assay using simple sequence repeats (SSRs) to discriminate among different pathogen populations was validated. F. proliferatum was isolated from onion and soil samples from the affected field, nearby agricultural fields and natural vegetation in southern Israel onion production areas. Fungal isolates were obtained also from onion sets (grown in northern Israel and shipped for planting in southern fields), to test a hypothesis that the fungus was disseminated on these sets. SSR analyses revealed that fungal populations from onion sets in northern Israel are genetically distinct from those in southern Israel. F. proliferatum populations from southern field site soils are similar to one another and to those from bulbs at each of four southern fields. By SSR analysis, F. proliferatum isolates from volunteer salt cedars in the onion fields are clonal and indistinguishable from those from the southern field soil and white onion bulbs. The findings suggest that onion sets purchased from northern Israel are not the source of the F. proliferatum causing onion salmon blotch in southern Israel. Furthermore, volunteer weeds, including salt cedar, and previously contaminated field soil could serve as alternative reservoirs for the fungus, from which inoculum could have moved to the onions
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- OSU Dissertations [11222]