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Ecology and Epidemiology

Distribution and Efficacy of Propagules of Verticicladiella procera in Soil. Kathy J. Lewis, Graduate research assistant, Department of Plant Pathology, Physiology and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg 24061, Present address: Ministry of Forests, Pest Management Division, Prince George, BC, Canada; S. A. Alexander(2), and W. Elliott Horner(3). (2)(3)Associate professor, and graduate research assistant, respectively, Department of Plant Pathology, Physiology and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg 24061, (3)Present address: Tulane Medical Center, 1500 Perdido St., New Orleans, LA 70112. Phytopathology 77:552-556. Accepted for publication 4 September 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-552.

The importance of soilborne propagules for spread of Verticicladiella procera in Christmas tree plantations was studied by examining propagule distribution in soil and their capability to cause disease. The distribution of soilborne propagules was closely associated with colonized roots of Pinus strobus and P. sylvestris Christmas trees. Propagule numbers were greatest in soil at the root collar (812 101 propagules per gram of soil) and decreased logarithmically toward the root tip (fewer than 40 propagules per gram at 30 cm). This distribution reflected the pattern of colonization in the root. No propagules were found near the roots of asymptomatic trees. Twelve seedlings were planted at 10, 25, and 40 cm from the root collar of each of four diseased trees. Colonization of seven seedlings was related to proximity to the root collar rather than to presence of detectable levels of V. procera in soil. Colonized roots appeared to be the source of propagules in soil, and these propagules were determined to be relatively unimportant for pathogen spread. The presence of conidiophores of V. procera in weevil galleries in roots of diseased trees, observation of weevil feeding signs on seedling stems, and the colonization of a potted seedling in the vicinity of diseased trees suggest that insects (Coleoptera) are potentially important vectors of V. procera.