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First Report of Verticillium dahliae Causing Artichoke Wilt in California

In mid-August 1998, artichoke (Cynara scolymus L.) plants of cultivar Imperial Star in a field in the Salinas area of the central coast of California developed wilt symptoms. The plants were stunted with chlorotic, drooping, and dried leaves near the bottom and middle of the plants as previously described in Italy (1). Diseased plants produced smaller edible buds and, in severe cases, buds were discolored with dried outer bracts. Roots exhibited the characteristic vascular discoloration of Verticillium infection. In one part of the infested field, artichoke was near harvest with 85% of plants showing wilt symptoms with vascular discoloration whereas the other part had a 60-day-old crop with 98% of plants infected. Yield in the field was reduced by as much as 50%. Verticillium dahliae was isolated from infected plant samples on NP-10 medium (2), and isolates were single spored before storing on potato dextrose agar at 4°C. Identity of the pathogen was confirmed based on colony morphology and formation of microsclerotia. In root-dip inoculation tests in the greenhouse, two V. dahliae isolates from artichoke infected 1-month-old artichoke seedlings that wilted within 6 weeks of inoculation. V. dahliae was reisolated from plants showing vascular discoloration. Cross-inoculation studies revealed that artichoke isolates caused a moderate level of disease in lettuce, but only a trace of vascular discoloration in cauliflower. Lettuce isolates caused a severe wilt in artichoke. Cauliflower isolates did not cause wilt in lettuce and caused only slight vascular discoloration in artichoke. This is the first report of a Verticillium wilt of artichoke in California.

References: (1) M. Cirulli et al. Plant Dis. 78:680, 1994. (2) L. H. Sorensen et al. Phytopathology 81:1347, 1991.