Disease Note

Verticillium Wilt (Verticillium albo-atrum) of Alfalfa in Minnesota. F. I. Frosheiser (deceased), USDA-ARS, Department of Plant Pathology, University of Minnesota, St. Paul 55108, and E. H. Hijano, INTA. E. E. A. Manfredi, 5988 Manfredi, CBA, Argentina. Plant Disease 69:268, 1985. Accepted for publication 8 November 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-268c.

Verticillium wilt of alfalfa (Medicago sativa L.) caused by Verticillium albo-atrum Reinke & Berth. has been a destructive disease in northern Europe for several decades and was identified in the Pacific Northwest of the United States in 1976 and in Wisconsin in 1980.  In July 1981, wilted plants with typical symptoms of the disease were observed in experimental alfalfa plots in Rosemount, Minnesota.  V. Albo-atrum was isolated on ethanol-streptomycin agar from stem and root tissue of the wilted plants.  The isolates formed conidia and dark resting mycelia when grown on prune-lactose-yeast agar, and conidial suspensions of V. albo-atrum were produced in Czapek-Dox broth on a reciprocating shaker.  Roots of cv. Saranac plants were immersed in conidial suspensions (About 8 × 10⁶ conidia per milliliter) of each of five isolates for 20 min, then transplanted into clay pots in the greenhouse.  Wilted shoots appeared in 3 wk, and V. albo-atrum was reisolated from stems of wilted plants.  The fungus was subsequently isolated in four alfalfa fields in Carver County, Minnesota, and in experimental plots in Sherburne County in October 1981.  Stands in which Verticillium wilt was observed were 3 yr old or older, with the exception of one 2-yr-old alfalfa field.  Additional surveys are necessary to determine the extent and importance of the disease in Minnesota.

References: Graham, J. H., et al. Plant Dis. Rep. 61:337, 1977.  Grau et al. Plant Dis. 65:843, 1981.