Department of Molecular Biology and Genetics
Department of Horticultural Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada
Department of Molecular Biology and Genetics, University of Guelph, Guelph, Ontario N1G 2W1, Canada
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Accepted for publication 23 February 2001
A potato breeding population was evaluated for the presence of tolerance and resistance to Verticillium dahliae. Clones were ranked as susceptible or moderately and highly resistant based on symptom expression, and a species-specific polymerase chain reaction (PCR)-based assay was used to determine the Verticillium biomass in the bases of stems. A clone was designated as tolerant if the amount of fungus present in the host tissue was equal to or greater than the collective average amount for all clones in the symptom category above. Tolerant and resistant clones were identified in all trials, but the expression of tolerance was usually unstable across runs. The fungus was detected in some symptomless plants; on the other hand, some symptomatic plants were found to be pathogen-free. These observations emphasize the necessity of accurate quantification of the pathogen biomass in potato during Verticillium resistance breeding programs.
© 2001 The American Phytopathological Society