VIEW ARTICLE

Ecology and Epidemiology

Identification and Pathogenicity of Some Alaskan Isolates of Armillaria. Charles G. Shaw III, Research plant pathologist, U.S. Department of Agriculture Forest Service, Forestry Sciences Laboratory, Pacific Northwest Forest and Range Experiment Station, Juneau, AK, Current address: U.S. Department of Agriculture Forest Service, Rocky Mountain Forest and Range Experiment Station, 240 West Prospect, Fort Collins, CO 80524; E. M. Loopstra, Biological technician, U.S. Department of Agriculture Forest Service, Forestry Sciences Laboratory, Pacific Northwest Forest and Range Experiment Station, Juneau, AK. Phytopathology 78:971-974. Accepted for publication 17 February 1988. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988. DOI: 10.1094/Phyto-78-971.

Twenty-six isolates of Armillaria spp. were collected in Alaska from mushroom stipes, spores, decayed wood, and rhizomorphs and paired in culture with haploid tester strains of the known North American biological species (NABS) of Armillaria. The NABS of isolates obtained from wood and rhizomorphs could not be determined by these tests, but NABS V and IX were identified from material for which single-spore isolates were available. Several isolates also were tested for pathogenicity on seedlings of Alaska-cedar and Sitka spruce. None of the four isolates tested on Alaska-cedar infected any seedlings even though all of these isolates were obtained from dying Alaska-cedars and nearly all inoculum segments produced abundant rhizomorphs. On Sitka spruce, the three diploid isolates obtained from wood were significantly more pathogenic than the two diploid isolates obtained from sporophore stipes. In addition, single-spore isolates of both NABS V and IX caused more infections on Sitka spruce than did their diploid parent isolates. A statistical analysis of previously published but unanalyzed data also indicated that single-spore isolates may be as pathogenic, and in some cases more pathogenic, than field-collected, diploid isolates.