First Report of Armillaria sinapina, a Cause of Armillaria Root Disease, Associated with a Variety of Forest Tree Hosts on Sites with Diverse Climates in Alaska.

In August of 2007, a preliminary survey was conducted in Alaska to evaluate potential impacts of climate change on forest trees. Armillaria sinapina, a root-disease pathogen, was isolated from conifer and hardwood hosts on climatically diverse sites spanning 675 km from the Kenai Peninsula to the Arctic Circle. Seven isolates (NKAK1, NKAK2, NKAK5, NKAK6, NKAK9F, NKAK13, and NKAK15) were identified as A. sinapina by using intergenic spacer-1 nucleotide sequences (GenBank Accession Nos. EU665175-EU665181) and somatic pairings. Of particular note is that one isolate (NKAK9F) was obtained from a declining Salix sp. (willow) growing in a flood plain near the Arctic Circle (66°32.316'N, 150°47.717'W). This isolate was collected from mycelial bark fans that were intercalated within multiple bark layers, a sign of disease. All other isolates were derived from rhizomorphs attached to and/or embedded within roots and root collars, but most host trees showed no clear indication of disease. Two isolates were collected from dead trees within a small mortality center (62°08.703'N, 150°04.593'W) that included an isolate from Picea glauca (white spruce; NKAK13) and another isolate from Betula sp. (birch; NKAK15). Additional isolates came from a beetle-killed P. glauca (NKAK1) 120 km northwest of Anchorage (61°48.079'N, 148°16.983'W) and a suppressed (overtopped by other trees in the stand) Tsuga mertensiana (mountain hemlock; NKAK2) 58 km southeast of Anchorage (60°50.679'N, 149°03.742'W). The two remaining isolates originated from the Kenai Peninsula (approximately 60°29.629'N, 149°45.465'W) and were derived from a root-diseased Populus tremuloides (trembling aspen; NKAK5) and a suppressed P. glauca (NKAK6). Although A. mellea sensu lato was previously reported on willow in interior Alaska (1) and A. sinapina was previously reported from sites under coastal influence (4), this represents the first confirmed report of A. sinapina on P. glauca, T. mertensiana, Populus tremuloides, Salix sp., and Betula sp. in Alaska. Unfortunately, pathogenicity of A. sinapina cannot be readily verified under experimental conditions because environmental variables, host-tree status (e.g., species, population, age, and vigor), and inoculum potential are difficult to recreate. Armillaria sinapina is typically regarded as a weak pathogen of diverse hosts (3). However, A. sinapina is predicted to cause more disease on hosts predisposed by climate stress, and climate change is well-documented in Alaska (2). Because A. sinapina occurs on diverse hosts under different climates across a wide geographic range in Alaska, Armillaria root disease could become more prevalent on trees stressed by climate change. References: (1) T. E. Hinds and T. H. Laurent. Plant Dis. Rep. 62:972, 1978. (2) J. J. McCarthy et al., eds. Climate Change 2001: Impacts, Adaptation and Vulnerability. Cambridge University Press, Cambridge, 2001. (3) D. J. Morrison et al. Can. J. Plant Pathol. 7:242, 1985. (4) C. G. Shaw, III and E. M. Loopstra. Phytopathology 78:9714, 1988.