Evaluation of Mint Mutants, Hybrids, and Fertile Clones for Resistance to Verticillium dahliae.

Peppermint and spearmint clones derived from cobalt 60 gamma irradiation and peppermint seed fertile clones and hybrids were evaluated for resistance to Verticillium dahliae in inoculation tests in the greenhouse. Mutant and fertile clones and hybrids varied significantly for wilt resistance. One peppermint mutant clone, three peppermint hybrids, and four peppermint fertile clones had low but varying wilt-severity values. Native spearmint and mutant lines derived from native spearmint had high levels of resistance. The wilt-severity scale used to assess disease levels was correlated with the number of CFU of V. dahliae from inoculated stems.