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Verticillium Wilt of Alfalfa in California. T. R. Gordon, Department of Plant Pathology, University of California, Berkeley 94720. J. C. Correll, D. G. Gilchrist, and A. N. Martensen. Department of Plant Pathology, University of California, Berkeley 94720, and Department of Plant Pathology, University of California, Davis 95616. Plant Dis. 73:18-20. Accepted for publication 20 May 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0018.

Verticillium wilt of alfalfa, caused by Verticillium albo-atrum, has been identified in three coastal counties of central and northern California. The disease appears to be well established in these areas. In contrast, a survey of alfalfa fields in 11 counties of the San Joaquin and Sacramento valleys did not identify any Verticillium-wilt infected plants. Twenty cultivars and experimental lines were tested for their reactions to a California isolate of V. albo-atrum at two inoculum concentrations by a root dip assay conducted in a greenhouse. Rankings of the entries at the two inoculum concentrations based on a visual symptom severity index were highly correlated (r = 0.866). Rankings of resistant and susceptible control entries were similar to reactions previously reported for isolates from other states. Several semidormant and nondormant entries for which disease reactions had not been reported previously showed a high level of resistance to Verticillium wilt. On the basis of these results and recently published information on host range and vegetative compatibility, the California isolate was indistinguishable from those previously reported in North America.