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Influences of Cropping Practices on Verticillium dahliae Populations in Commercial Processing Tomato Fields in Ontario

First author: Department of Plant Sciences, Biological and Geological Sciences Building, The University of Western Ontario, London, ON, Canada N6A 5B7; and second author: Agriculture and Agri-Food Canada, Southern Crop Protection & Food Research Centre, London, ON, Canada N5V 4T3, and Departments of Plant Sciences and Microbiology and Immunology, The University of Western Ontario, London, ON, Canada N6A 5B7

The abundance of Verticillium dahliae in the soil and the incidence of V. dahliae-infected plants were determined for 12 commercial processing tomato fields in Kent County, Ontario. Comparison of the data with those from a previous survey of fields in adjacent Essex County showed that soil inoculum levels and incidence of infection were generally lower in Kent County fields and that race 2 V. dahliae was not common in Kent County. From the two counties, 128 isolates were characterized by restriction fragment length polymorphism (RFLP) analysis, using the subspecies-specific repetitive DNA sequence E18. A subset of these isolates was also characterized by vegetative compatibility and DNA hybridization analysis with a second subspecies-specific DNA sequence. Isolates with E18 RFLP profiles highly similar to those of isolates previously collected from potato fields in North America were prevalent in Essex County tomato fields but not common in Kent County fields. The data are consistent with the hypothesis that the group I isolates were introduced into southwestern Ontario with potato and that the different cultural practices in Essex County and Kent County have contributed to the differences in the accumulation of these isolates in the two regions.

Additional keyword: Verticillium wilt.