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Persistence and Distribution of a Clone of Armillaria mellea in a Ponderosa Pine Forest. Charles G. Shaw III, Former Graduate Research Assistant, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331, Senior authorís present address: Forest Research Institute, Private Bag, Rotorua, New Zealand; Lewis F. Roth, Professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Phytopathology 66:1210-1213. Accepted for publication 12 April 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1210.

Clonal relationships of isolates of Armillaria mellea from a heavily diseased ponderosa pine forest were tested in culture. Members of unrelated clones formed dark lines of demarcation between paired isolates. Lines did not form between paired members of the same clone. All isolates from within a 600-hectare area, which included several root rot infection centers, were found to belong to a single clone. Continuity of the clone over the area suggested that fungal distribution had been by vegetative growth from a single point of origin rather than by spores. Measurements of twenty infection centers disclosed an average radial growth rate of 1.0 m/year. Calculations indicated that the clone had been spreading vegetatively for at least 460 years.

Additional keywords: barrage reaction, mutual aversion, fungal genotypes, fungal growth rate, food base, epidemiology.