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Ecology and Epidemiology

Host Specialization of Three Morphological Variants of Verticicladiella wageneri. T. C. Harrington, Former graduate research assistant, Department of Plant Pathology, University of California, Berkeley 94720, Present address: Dept. of Botany and Plant Pathology, University of New Hampshire, Durham 03824; F. W. Cobb, Jr., professor, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 74:286-290. Accepted for publication 15 September 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-286.

Inoculations of seedlings and mature trees of ponderosa pine and Douglas-fir with 28 isolates of Verticicladiella wageneri, cause of black stain root disease, demonstrated host preferences of three morphological variants of the pathogen. Although each isolate tested was capable of infecting both hosts, isolates of the hard pine variant (isolated primarily from ponderosa, Jeffrey, and lodgepole pines) consistently infected more pine seedlings and older ponderosa pines than did isolates of the Douglas-fir variant (isolated from Douglas-fir). The converse occurred with Douglas-fir. Isolates of the third variant (isolated only from pinyons) were generally intermediate between isolates of the other two variants in pathogenicity on seedlings of both hosts. Few seedlings of sugar pine or western hemlock were infected by any of 10 isolates that were selected from the hard pine and Douglas-fir variants. Two-way analysis of variance showed significant host species morphological variant interaction in two seedling-inoculation experiments and in one field-inoculation experiment, which demonstrates that these variants preferentially infect and colonize their respective hosts. The variants also differed in survival when colonized blocks were buried in nonsterile soil at 21 and 27 C. The possible role of temperature in the restriction of the hard pine variant to relatively cool sites is discussed.