The reaction of 14 populations of Agastache maintained at the North Central Regional Plant Introduction Station to Verticillium wilt was evaluated. The plants were inoculated by root dip with 3 strains of Verticillium dahliae: peppermint, potato, and Agastache. Infected plants were obtained only from inoculation with the Agastache strain of Verticillium. Agastache rugosa had a higher rate of infection (10-21%) than Agastache foeniculum and Agastache nepetoides, both with infection rates ≤ 5 percent. A pathogenicity test of the Agastache strain of Verticillium conducted on various species of the mint family resulted in clear symptoms of disease, such as leaf curling, plant wilting, and death in individuals of Pycnanthemum pilosum and Salvia azurea. Internal infection with Verticillium was also detected in 1 species of Calamintha (14%) and 3 species of Ocimum (38-54%). Results of this study revealed interspecific variability for susceptibility to Verticillium among species of Agastache. The possible specificity of the Agastache strain of Verticillium is also supported by our results.
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