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Relatedness and Spatial Distribution of Armillaria Genets Infecting Red Pine Seedlings. Myron L. Smith, Department of Botany, University of Toronto, Erindale College, Mississauga, Ontario L5L 1C6, Canada, Present address: Department of Botany, Biotechnology Laboratory, University of British Columbia, Vancouver, V6T 1Z4, Canada.; Johann N. Bruhn(2), and James B. Anderson(3). (2)Department of Plant Pathology, University of Missouri, Columbia 65211; (3)Department of Botany, University of Toronto, Erindale College, Mississauga, Ontario L5L 1C6, Canada. Phytopathology 84:822-829. Accepted for publication 29 April 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-822.

Genetic similarity among Armillaria genets responsible for root disease foci in a northern Michigan red pine plantation was investigated. The study plantation was established in 1984 in a clear-cut portion of a 60-yr-old hardwood forest. Armillaria isolates obtained from 87 moribund seedlings were examined. All 87 isolates were identified as A. ostoyae on the basis of mitochondrial DNA (mtDNA) restriction fragment patterns and/or mating interactions with voucher isolates. Independent assays of nuclear DNA restriction fragment patterns and somatic incompatibility groups agreed completely in distinguishing genets at the study site. Given knowledge of the stand history and previous estimates of mycelial growth rates, we conclude that several genets occupying large territories must have been established long before the 1984 stand conversion. Genetic similarity estimates were made by examining 83 nuclear DNA restriction fragment markers in 16 A. ostoyae genets within the plantation and an additional four A. ostoyae genets sampled outside the plantation. Together with data on the distribution of mtDNA types, these nuclear DNA similarity estimates are consistent with the hypotheses that 1) mtDNA (maternal) lineages exist in the local population; 2) members of the population were established by effectively anisogamous sexual mating events; and 3) the breeding population of A. ostoyae at this site extends beyond 1 km.

Additional keywords: DNA fingerprinting, forest pathology.