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Use of Taxon-Specific Competitive-Priming PCR to Study Host Specificity, Hybridization, and Intergroup Gene Flow in Intersterility Groups of Heterobasidion annosum. Matteo Garbelotto, Department of Environmental Science, Policy, and Management, University of California, Berkeley 94720; Alice Ratcliff(2), Thomas D. Bruns(3), Fields W. Cobb(4), and William J. Otrosina(5). (2)Pacific South Western USDA Forest Service Research Laboratory, Albany, CA 94710; (3)(4)Department of Environmental Science, Policy, and Management, University of California, Berkeley 94720; and (5)United States Forest Service, Forest Science Laboratory, Institute for Tree Root Biology, 320 Green St., Athens, GA 30602. Phytopathology 86:543-551. Accepted for publication 13 February 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/Phyto-86-543.

Two intersterility groups (ISGs) of the forest pathogen Heterobasidion annosum are found in California: S and P. We devised a polymerase chain reaction (PCR) method called taxon-specific competitive-priming (TSCP) PCR to differentiate the two ISGs. Using TSCP-PCR, we typed 537 live isolates and dry basidiocarps from 204 trees and 114 stumps from 60 sites in eight California national forests. All isolates from fir and sequoia stumps or trees were S; isolates from pine stumps were 80% S and 20% P; isolates from pine, incense cedar, and western juniper trees were 23% S and 77% P. The recovery of a well-established hybrid “SP” genet in a pine center was confirmed by isozyme analysis. The PCR amplification of the mitochondrial ML5-ML6 region also was diagnostic for the two ISGs, but in areas where both fir and pine mortality centers were present, about 7% of S isolates yielded the P-specific fragment. These results indicate the possibility of gene flow in nature between the two ISGs. The presence of S isolates on trees previously regarded as exclusive P hosts broadens the potential host range of this ISG.