First Report of the Root-Rot Pathogen, Armillaria nabsnona, from Hawaii

Abstract

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.

Forest root diseases across the United States

“…In Alaska and the Southern Region, Armillaria is not usually the primary cause of tree mortality, but is an opportunist on many tree species affected by other factors. In Hawaii, Armillaria species have been found associated with declining stands, but the overall incidence on the Hawaiian islands is unknown (Hanna et al 2007;Kim et al 2010).…”