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Resistance

Distribution of Verticillium in Stems of Resistant and Susceptible Species of Mint. W. H. Brandt, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331; M. L. Lacy(2), and C. E. Horner(3). (2)(3)Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331, (2)Present address: Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Phytopathology 74:587-591. Accepted for publication 17 November 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-587.

Two methods were used to ascertain whether the ascent or proliferation of Verticillium dahliae is retarded in the stems of the resistant Mentha crispa compared to that in the susceptible Mentha piperita. In the greenhouse, young cuttings of both mint species were planted in soil artificially infested with V. dahliae. Surface-sterilized nodes of these plants were plated out on agar weekly and the presence of V. dahliae was ascertained for each node. In the field, rooted cuttings were planted into heavily infested soil; once a week, the stem of each sampled plant was cut into segments and the segments were individually fragmented in a small amount of distilled water. The resulting suspension was plated out and the relative amounts of propagules of V. dahliae were ascertained. We detected no difference in the ascent of V. dahliae in stems of either mint species. However, two-thirds of the infected plants of M. piperita yielded from 100 to 15,000 propagules per millimeter of stem length. Most plants of M. crispa yielded fewer than 10 with a maximum of 57 propagules per millimeter of stem. Evidently, M. crispa suppresses the proliferation of V. dahliae, but not the ascent of the fungus, within the stems.