Disease Note.

Verticillium Wilt of Protea (Leucospermum cordifolium) Caused by Verticillium dahliae. S. T. Koike, University of California Cooperative Extension, Salinas 93901. J. H. Nelson, and D. K. Perry. T. B. Bishop Co., Goleta, CA 93117; and Perry’s Panorama, Somis, CA 93066. Plant Dis. 75:1074. Accepted for publication 20 May 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-1074E.

In commercial floriculture, "protea" refers to the cut flowers produced by many genera of the Proteaceae. In California, approximately 203 ha are planted commercially, and the estimated value of the harvested commodity is over $5 million. In 1989 in Santa Barbara County, plants of pincushion protea (Leucospermum cordifolium (J. Knight) Fourc.) in commercial fields began to collapse and to die. Symptoms on these plants, which had been in the field for 16 mo, consisted of terminal shoot wilting, fading of foliage to light green, and eventual collapse and browning of the entire plant. Brown flecking and streaking also appeared in the stem xylem tissue. Isolations onto acidified potato-dextrose agar consistently produced Verticillium dahliae Kleb. with characteristic verticillate conidiophores and black micro sclerotia. Pathogenicity was tested on rooted cuttings of L. cordifolium cv. Firewheel that were grown in a greenhouse for 10 mo. The roots of 10 of these plants were sliced with a razor, dipped in a spore suspension (1 X 10⁶ conidia per milliliter) of one of the V. dahliae isolates, and repotted. Roots of control plants were cut and dipped into distilled water. All plants were maintained in a greenhouse at 20-25 C. After 8 mo, the foliage of inoculated plants desiccated and faded and vascular tissue had brown flecks. V. dahliae was reisolated from these plants. Control plants did not show any wilt symptoms. This is the first report of Verticillium wilt on any protea species. Other commercially grown protea species (Banksia victoria, Leucodendron salignum, Protea compacla, P. cynaroides, P. eximia, P. magnifica, and P. neriifolia) were inoculated with V. dahliae by the same method, but only B. victoria (woolly orange banksia) developed wilting symptoms and became infected with the pathogen.