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Persistence of an Alfalfa Strain of Verticillium albo-atrum in Soil. A. P. Keinath, Graduate research assistant, Department of Plant Pathology, Cornell University, Ithaca, NY 14853; R. L. Millar, professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 76:576-581. Accepted for publication 3 January 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-576.

The potential of an alfalfa strain of Verticillium albo-atrum to survive in the absence of alfalfa (Medicago sativa) was tested in unsterile soil collected from a field of alfalfa severely affected with Verticillium wilt. Propagules added to soil were distinguished from indigenous propagules of Verticillium spp. by use of a benomyl-tolerant isolate. Dark mycelium, conidiophores, and conidia were produced on alfalfa stems buried in soil in petri plates at -0.01, -0.3, or -3.0 bars φm and 6 and 21 C, but production was reduced in soil at -0.01 bar. The number of conidiophores decreased significantly (P < 0.05) between 4 and 16 wk after burial. Numbers of conidia declined after 5 wk in soils held at φm ≥ 1.0 bar. Saprophytic capability of V. albo-atrum in unsterile soil was limited. The distance that V. albo-atrum grew through soil was 5 mm and < 12% of available healthy tissue was colonized. The pathogen persisted in infected alfalfa stems in a field from November to October, but only 3% of the tissue remaining after 11 mo yielded V. albo-atrum.