Relatedness and spatial distribution of Armillaria genets infecting red pine seedlings

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