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Verticillium Wilt of Cauliflower in California. STEVEN T. KOIKE, University of California Cooperative Extension, Salinas 93901. KRISHNA V. SUBBARAO, Department of Plant Pathology, University of California, Davis, c/o U.S. Agricultural Research Station, Salinas 93905; R. MICHAEL DAVIS, Department of Plant Pathology, University of California, Davis 95616; THOMAS R.GORDON, Department of Plant Pathology, University of California, Berkeley 94720; and JUDITH C.HUBBARD, Department of Plant Pathology, University of California, Davis, c/o U.S. Agricultural Research Station, Salinas 93905. Plant Dis. 78:1116-1121. Accepted for publication 11 July 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-1116.

Since 1990. commercial cauliflower in coastal California has been severely affected by a vascular will disease. Symptoms consist of chlorosis, defoliation, stunting, willing, and vascular discoloration. Disease has been widespread and has caused significant damage in summer and fall crops. Verticillium dahliae was consistently isolated from xylem tissue in stems and roots of affected plants. Techniques tested for inoculation of cauliflower plants were dipping clipped or nonclipped roots into spore suspensions, injecting spore suspensions into cauliflower stems, and planting seedlings into soil along with an agar block colonized with microsclerotia. Only dipping roots into spore suspensions was consistently successful in causing Verticillium wilt. Pathogenicity was established by dipping roots of 30-day-old seedlings of cauliflower cv. White Rock into conidial suspensions (107 conidia per millilitcr) for 5 min. Control plants were dipped into sterile distilled water. All plants were potted into autoclaved soil and incubated both in a growth chamber (20 1/15 plus or minus 1 C day/night regime) and in a greenhouse (23 plus or minus 1/10 plus or minus 1 C day/night regime). After 4 wk, inoculated plants were stunted and chlorotic and V. dahliae was reisolaled, whereas control planls were symptomless and V. dahliae was not reisolatcd. When incubation temperature maxima in the greenhouse exceeded 30C, inoculated plants failed to show symptoms. Soil from commercial fields was assayed for microsclerotia on NP-10 selective medium using the modified Anderson sampler. V. dahliae was widely distributed in the Salinas Valley, with propagule densities as high as 93 microsclerotia per gram of soil. Evaluation of cauliflower cultivars in V. dahlia-infested fields indicated that all were susceptible. 1 his new disease has become a major threat to cauliflower production in coastal California.

Keyword(s): cole crops, cultural practices, disease management, resistance