WWETAC Projects

Project Title: Developing an interior west-wide model to predict present and future climatic influences on Armillaria root disease in the USA

Principal Investigators: Ned Klopfenstein, USDA Forest Service, Rocky Mountain Research Station; Helen Maffei and Aaron Smith, USDA Forest Service, Region 6 Forest Health Protection; Mary Lou Fairweather, USDA Forest Service, Region 3 Forest Health Protection

Collaborators: Robert L. Mathiasen  and Erik Nelson, Northern Arizona University, School of Forestry; Mee-Sook Kim, Kookmin University, Seoul, Korea; John Hanna and Sara Ashiglar, USDA Forest Service, Rocky Mountain Research Station; Amy Ross-Davis, Western Forestry and Conservation Association, Geral McDonald, (emeritus) USDA Forest Service, Rocky Mountain Research Station.

Key Issues/Problems Addressed:

Armillaria root disease (caused by the fungal pathogens in the genus Armillaria) has a worldwide distribution, affecting extremely diverse tree species and causing major damage in western North America. Accurate identification and documented distribution of Armillaria pathogens across diverse landscapes is needed for predicting Armillaria spp. distribution and activity, especially given its predicted increase with climate change.

Setting and Approach:

Random-plot surveys were conducted across climatically diverse sites to determine baseline distribution data for Armillaria species on diverse tree/shrub species in the East Cascades of Central Oregon. Armillaria spp. isolates were identified with DNA based techniques. (Additional surveys are continuing through 2010-2012 to document the distribution of Armillaria spp. in Arizona.) To further develop DNA-based identification, methods sequences of the translation elongation factor-1 alpha (EF-1α) gene were used to distinguish 30 isolates representing the ten North American Armillaria species.

Key Findings:

  • Armillaria spp. are common in the East Cascades of Oregon, occurring on 56 percent of 260 sampled plots. Armillaria incidence increases to 73 percent, when 95 of the driest, wettest, warmest, and coolest plots are excluded.
  • Among the three Armillaria species groups identified in the Eastern Oregon surveys, the North American Biological Species (NABS) X group was collected from the greatest range of climates as inferred from vegetation subseries. Armillaria solidipes group was rarely found on the warmest sites and the NABS III-V-VII (A. calvescens-A. sinapina-A. gallica) complex was rarely found on the coolest sites.
  • Partial sequence data for the EF-1α gene delineated all ten North American species of Armillaria into separate genetic groups or subgroups, but A. gallica isolates were comprised within multiple genetic subgroups.
  • Multiple Armillaria species have been found in ongoing surveys of Arizona


Baseline information presented on Armillaria spp. in the Oregon East Cascades and Arizona will help develop models to predict the potential distribution of Armillaria root disease pathogens under current and changing climates. Additionally, DNA sequences of EF-1α may serve as a useful diagnostic tool to accurately identify Armillaria spp., which will help differentiate virulent root disease pathogens from beneficial saprophytes.


Hanna, J.W.; Smith, A.L.; Maffei, H.M.; Kim, M.-S.; Klopfenstein. N.B. 2009. Survey of Armillaria spp. in the Oregon East Cascades: Basline data for predicting climatic influences on Armillaria root disease. pp. 53-59 in: Baker, F., comp. Proc 56th Annual WIFDWC. 27-31 October 2008, Missoula, MT, USA. (PDF, 1.54 MB)

McDonald, G.I.; Hanna, J.W.; Smith, A.L.; Maffei, H.M.; Kim, M.-S.; Ross-Davis, A.L.; Klopfenstein, N.B. 2011. Preliminary report on the ecology of Armillaria in the East Cascades of Oregon. pp. 135 - 138 in: Fairweather, M. comp. Proc. of the 58th annual Western International Forest Disease Work Conference,  4-8 October 2010, Valemount, BC, Canada. (PDF, 2.55 MB)

Ross-Davis, A.L.; Hanna, J.W.; Kim, M.-S.; Klopfenstein, N.B. 2012. Advances toward DNA-based identification and phylogeny of North American Armillaria species using elongation factor-1 alpha gene. Mycoscience 53: 161-165.

WWETAC Project ID:  FY10TS72