VIEW ARTICLE

Etiology

Pathogenicity of Leptographium and Verticicladiella spp. Isolated from Roots of Western North American Conifers. T. C. Harrington, Graduate research assistant, Department of Plant Pathology, University of California, Berkeley 94720; F. W. Cobb, Jr., professor, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 73:596-599. Accepted for publication 6 October 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-596.

Fourteen isolates representing seven species of Verticicladiella and Leptographium were used in greenhouse pathogenicity tests on wounded and unwounded ponderosa pine and Douglas-fir seedlings. Although each of these fungus species has been isolated from roots showing symptoms of black-stain root disease, only isolates of V. wageneri reproduced the unique symptomatology of the disease. Colonization by V. wageneri was predominantly vertical with hyphae in the tracheids, but not in xylem parenchyma. Most of the other species tested showed some degree of pathogenicity but, unlike V. wageneri, generally required wounds for infection counts. Also, their hyphae were found in both tracheids and parenchyma. Three of the fungi (L. terebrantis, V. abietina, and an unidentified Verticicladiella sp.) were isolated from common root- and stump-feeding bark beetles known to be active in roots infected by V. wageneri. It appears that only V. wageneri is capable of causing black-stain root disease, and that other fungi isolated from black-stained tissues are secondary invaders introduced into diseased roots by bark beetles.