Laminated Root Rot Research Recommended

On January 9, the Washington State Academy of Sciences presented its special report, “Opportunities for addressing laminated root rot caused by Phellinus sulphurascens in Washington’s Forests,” to Commissioner of Public Lands Peter Goldmark. The academy was formed in 2005 and is comprised of Washington’s leading scientists and engineers. Its two-fold mission is: provide expert scientific and engineering analyses to public policy makers in Washington State, and increase the role and visibility of science.

Washington Academy of Sciences study
(from left) Commissioner of Public Lands Peter Goldmark, Dr. R. James Cook, and Dr. Robert Edmonds present the Washington Academy of Sciences study on laminated root rot at a state Senate hearing in early February 2014. Photo: Diana Lofflin/DNR.

The report was requested by Commissioner Goldmark in 2011 to determine which forest tree root diseases would be best suited for further scientific research and applied management. Commissioner Goldmark is by law Washington’s leader for all forest health issues in the state. He recognized that forest root diseases are among the most vexing, persistent problems for forest management, and are likely to have increasingly serious effects as trees are stressed by anticipated climate changes. The contents and advice in the report are important and timely for forest management and research.

The academy’s committee was chaired by Dr. R. James Cook (Professor Emeritus of Plant Pathology, Washington State University). Members were chosen for their competence in forestry, root diseases, and new research techniques, especially molecular biology. Other researchers contributed to the effort and the report was peer-reviewed.

A number of root diseases occur in Washington State but the committee decided to focus on laminated root rot caused by Phellinus sulphurascens because it is:

  • Relatively localized to Washington, Oregon, British Columbia, and small parts of Idaho, Montana and northern California;
  • Mostly a disease of Douglas-fir, killing trees and slowing their growth;
  • Affects the income-producing land of the Washington Department of Natural Resources (DNR);
  • Characterized by stable genets (clones); and
  • Represents a relatively simple pathosystem for obtaining data that could be applied to other forest root diseases.
Cream or yellow to cinnamon colored mycelium
Cream or yellow to cinnamon colored mycelium is found on the outer bark of roots with laminated root rot. Cathy Stewart/US Forest Service/Bugwood.org

Laminated root rot has major impacts on the income-producing land of the Washington Department of Natural Resources (DNR), causing economic losses of between 5 percent and 15 percent to Douglas-fir forestry. Based on the Douglas-fir that was harvested from State Trust Lands between July 2009 and June 2011, the lower estimate of losses (5 percent) amounts to 39 million board feet of timber (enough to build 2,437 homes) and $10.35 million – revenue that is not available every two years.

Laminated root rot causes trees to fall, which endangers roads, homes, campgrounds and people. The presence of the disease has led to tree removals and use changes recently at Lake Wenatchee, Millersylvania, Kopachuck and Lake Easton state parks.

Douglas-fir, western hemlock and several other conifer trees are susceptible to this native fungus which can persist for more than 40 to 50 years in roots and stumps. The disease spreads by root-to-root contact; adjacent tree roots that come in contact with the infected material get infected.

If an infected site is harvested, then replanted with Douglas-fir, the disease is likely to increase its presence in the stand, killing young trees, which sets back forest regeneration and reduces future productivity.

The major findings in the report include:

  • Native forest root diseases historically played beneficial roles in forest ecosystems by eliminating maladapted trees, fostering decomposition and nutrient cycling, creating wildlife habitat, and promoting ecological succession. However, in managed forests root diseases contribute to major losses in forest growth and hence major losses of revenue from timber sales. Climate change is likely to make these losses greater.
  • DNR should implement management practices to keep laminated root rot at endemic levels, document its presence, and reduce its impact on Trust assets.
laminated root diease
A Douglas-fir displays signs of laminated root disease (Phellinus weirii) Photo: Steve Wilent, Society of American Foresters, Bugwood.org.

The committee identified a number of opportunities to use existing and emerging tools in molecular genetics and genomics to better understand the dynamic ecological interactions that contribute to forest root diseases and open new approaches to its management. Exciting new research questions emerged. For example, why are some strains of the fungus active and virulent while others are quiescent? Does virulence get turned on and turned off? How does the fungus present in dead woody material get activated when a susceptible new root comes near? How does the fungus penetrate the barriers that usually protect living roots? What factors make some trees more resistant to the disease than others? What other microbes or organisms influence the behavior of the fungus and its host tree?

Specific research opportunities were identified including: investigating the population structure and phylogeography of P. sulphurascens, improving the means of rapidly identifying P. sulphurascens using PCR (Polymerase Chain Reaction); using transcriptomics to identify host defense and virulence genes; determining the genetically based resistance in populations of Douglas-fir; developing resistant clones of Douglas-fir; using metagenomics to characterize the microbiome of the rhizosphere of healthy and infected roots; and determining if naturally established seedlings are better adapted for fighting infection than nursery seedlings

The implementation of any these studies, however, represents a significant challenge in part because the capacity of the forest research community to conduct forest disease research and forest root disease research specifically, has diminished in recent years. There is now a complete absence of teaching of forest pathology in Washington State due to retirements at the state’s two research universities. This situation can only be alleviated by increasing the capacity of university forest pathology research and teaching, and by integrating forest pathology with other disciplines.

Karen Ripley, Forest Health Program Manager karen.ripley@dnr.wa.gov