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Ecology and Epidemiology

Genetic Relationships and Cross Pathogenicities of Verticillium dahliae Isolates from Cauliflower and Other Crops. K. V. Subbarao, Department of Plant Pathology, University of California, Davis, c/o U. S. Agricultural Research Station, Salinas 93905; A. Chassot(2), T. R. Gordon(3), J. C. Hubbard(4), P. Bonello(5), R. Mullin(6), D. Okamoto(7), R. M. Davis(8), and S. T. Koike(9). (2)(4)Department of Plant Pathology, University of California, Davis, c/o U. S. Agricultural Research Station, Salinas 93905; (2)Present address: Swiss Federal Institute of Technology, Universitatsstrasse 2, 8092 Zurich, Switzerland; (3)(5)(6)(7)Department of Plant Pathology, University of California, Berkeley 94720; (8)Department of Plant Pathology, University of California, Davis 95616; (9)University of California Cooperative Extension, Salinas 93901. Phytopathology 85:1105-1112. Accepted for publication 27 July 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/Phyto-85-1105.

Morphologies, genetic relationships, and host specificities of Verticillium dahliae isolates from artichoke, cabbage, cauliflower, cotton, pepper, potato, strawberry, tomato, and watermelon were evaluated. Temperature optima for mycelial growth were evaluated at 10, 15, 20, 25, 30, and 35ºC. Depending on the isolate, temperature optimum was either 20 or 25ºC. The length and width of conidia in isolates from crucifer crops were significantly greater than the dimensions of conidia in other isolates. Isolates from artichoke, cabbage, cotton, pepper, potato, strawberry, tomato, and watermelon were tested for their pathogenicity on their host of origin, as well as on cauliflower. In addition, two V. dahliae isolates from cauliflower were tested for their pathogenicity on all the above crops, lettuce, and other crucifer crops such as bok choi, broccoli, Brussels sprouts, napa cabbage, radish, and rapini. All isolates caused wilt on cauliflower. The cauliflower isolates caused various degrees of wilt on all crops except lettuce, but their virulence depended on the host inoculated. Cauliflower isolates were highly virulent on other crucifer crops except broccoli and Brussels sprouts, on which they were only weakly virulent. None of the isolates tested were host specific. Seventeen isolates of V. dahliae from noncruciferous hosts were associated with one of two vegetative compatibility groups. Twelve V. dahliae isolates from cruciferous crops could not be assigned to a vegetative compatibility group because they did not produce nitrate nonutilizing mutants when cultured on chlorate-containing media. This observation may reflect diploidy in the cruciferous isolates, an interpretation which was supported by conidial size and in situ measurements of conidial DNA content. Based on polymorphisms in the intergenic spacer region of the nuclear rDNA, the V. dahliae isolates from cauliflower were unlike isolates from other hosts.