Growth and Pathogenicity of Alfalfa Strain of Verticillium albo-atrum. A. A. Christen, Research Associate, Department of Plant Pathology, Washington State University, Irrigated Agriculture Research and Extension Center, Prosser 99350. R. C. French, Research Technician, Department of Plant Pathology, Washington State University, Irrigated Agriculture Research and Extension Center, Prosser 99350. Plant Dis. 66:416-418. Accepted for publication 15 August 1981. Copyright 1982 American Phytopathological Society. DOI: 10.1094/PD-66-416.

Thirty-eight isolates of Verticillium albo-atrum from alfalfa (Medicago sativa) from diverse locations in the northwestern United States and western Canada (British Columbia) appeared the same on prune lactose yeast agar. Eight isolates representative of this area were alike in growth response to temperature on prune lactose yeast agar; ability to induce symptoms in alfalfa cultivars Vertus (moderately resistant to V. albo-atrum) and Apalachee (susceptible to V. albo-atrum); pathogenicity to certain cultivars in eggplant (Solanum melongena), cantaloupe (Cucumis melo), and watermelon (Citrullus lanatus); and not inducing symptoms in potato (S. tuberosum) or tomato (Lycopersicon esculentum). The optimum temperature for growth in media was at or near 25 C. Growth of an isolate from alfalfa of V. albo-atrum on osmotically adjusted media was greater at 27 and 30 C than it was on the unamended agar medium. These observations indicate that only one alfalfa strain of V. albo-atrum exists in the area and that it may have the potential to become more widespread in the United States than strains of V. albo-atrum isolated from other crops.

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