Phylogenetic and genetic relationships among 10 North American Armillaria species were analysed using sequence data from ribosomal DNA (rDNA), including intergenic spacer (IGS-1), internal transcribed spacers with associated 5.8S (ITS + 5.8S), and nuclear large subunit rDNA (nLSU), and amplified fragment length polymorphism (AFLP) markers. Based on rDNA sequence data, the nLSU region is less variable among Armillaria species than the ITS + 5.8S and IGS-1 regions (nLSU < ITS + 5.8S < IGS-1). Phylogenetic analyses of the rDNA sequences suggested Armillaria mellea, A. tabescens and A. nabsnona are well separated from the remaining Armillaria species (A. ostoyae, A. gemina, A. calvescens, A. sinapina, A. gallica, NABS X and A. cepistipes). Several Armillaria species (A. calvescens, A. sinapina, A. gallica, NABS X and A. cepistipes) clustered together based on rDNA sequencing data. Based on the isolates used in this study, it appears that techniques based on IGS-1, ITS + 5.8S, and/or D-domain/3¢ ends of nLSU are not reliable for distinguishing A. calvescens, A. sinapina, A. gallica and A. cepistipes. However, AFLP data provided delineation among these species, and AFLP analysis supported taxonomic classification established by conventional methods (morphology and interfertility tests). Our results indicate that AFLP genetic markers offer potential for distinguishing currently recognized North American Biological Species (NABS) of Armillaria in future biological, ecological and taxonomic studies.

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.

The genus Armillaria (2) and Armillaria mellea sensu lato (3) have been reported previously from Hawaii. However, Armillaria species in Hawaii have not been previously identified by DNA sequences, compatibility tests, or other methods that distinguish currently recognized taxa. In August 2005, Armillaria rhizomorphs and mycelial bark fans were collected from two locations on the island of Hawaii. Stands in which isolates were collected showed moderate to heavy tree mortality and mycelial bark fans. Pairing tests (4) to determine vegetative compatibility groups revealed three Armillaria genets (HI-1, HI-7, and HI-9). Rhizomorphs of genet HI-1 were collected from both dead and healthy mature trees of the native 'Ohia Lehua (Metrosideros polymorpha) approximately 27 km west of Hilo, HI (approximately 19°40′49″N, 155°19′24″W, elevation 1,450 m). Rhizomorphs of HI-7 and HI-9 were collected, respectively, from dead/declining, mature, introduced Nepalese alder (Alnus nepalensis) and from an apparently healthy, mature, introduced Chinese banyan (Ficus microcarpa) in the Waipi'o Valley (approximately 20°03′29″N, 155°37′35″W, elevation 925 m). On the basis of somatic pairing tests and intergenic spacer-1 (IGS-1) nucleotide sequence identities of 99 to 100% with North American A. nabsnona (GenBank Accession No. AY509178), HI-1 (GenBank Accession No. DQ995356), HI-7 (GenBank Accession No. DQ995358), and HI-9 (GenBank Accession No. DQ995359) were identified as A. nabsnona, a pathogen of hardwoods (1). The IGS-1 sequences of A. nabsnona genets (HI-1, HI-7, and HI-9) had a greater similarity to North American collections of A. nabsnona than to the Asian A. nabsnona, even though the two introduced hosts originated from Asia. Phylogeographic studies could help determine the potential introduction and original source of A. nabsnona in Hawaii. Although A. nabsona was isolated from multiple hosts in declining stands, pathogenicity studies are needed to confirm whether this pathogen causes disease on diverse native and exotic tree species in Hawaii. References: (1) E. Allen et al. Pages 2–7 in: Common Tree Diseases of British Columbia. Natural Resources Canada. Canadian Forest Service, Victoria, BC, Canada, 1998. (2) D. E. Hemmes and D. E. Desjardin. Pages 129 and 153 in: Mushrooms of Hawaii. Ten Speed Press, Berkeley, CA, 2002. (3) F. F. Laemmlen and R. V. Bega. Plant Dis. Rep. 58:102, 1974. (4) Y. Wu et al. USDA Forest Service Tech. Rep. R2-58, 1996.