Genetics Provide Valuable Insight into Mysterious Decay Fungi

Valuable insights to developing effective biological control agents for protecting conifer trees from root rot have been discovered.

Pine log extensively colonized by Phlebiopsis gigantea showing fruiting structures from which spores are released. Photo: Robert Blanchette and Benjamin Held, University of Minnesota.

Pine log extensively colonized by Phlebiopsis gigantea showing fruiting structures from which spores are released. Photo: Robert Blanchette and Benjamin Held, University of Minnesota.

An international team of 41 scientists from eight countries, including USDA Forest Service Forest Products Laboratory (FPL) researcher Daniel Cullen, unraveled the longstanding mystery as to how the Phlebiopsis gigantea fungus rapidly colonizes wood to the exclusion of other invading microbes.

Daniel Cullen, FPL research microbiologist

Daniel Cullen, FPL research microbiologist

The devastating conifer pathogens in the Heterobasidion genus cause substantial economic damage to conifer roots in the Northern Hemisphere, by infecting stumps and wounded trees.  Another common and benign fungus, Phlebiopsis gigantea, is able to rapidly colonize conifer wood and prevent Heterobasidion species and other pathogens from taking hold.

Recently reported in the prestigious open access journal PLOS Genetics, “These findings pave the way for our deeper understanding of the complex and multifaceted biochemical pathways by which wood-degrading fungi metabolize wood and its constituents,” according to Professor Robert Blanchette of the University of Minnesota.

The unusual ability of Phlebiopsis gigantea to rapidly colonize freshly cut conifers has been known for decades. How the fungus tolerates and degrades the resins that conifer trees use as part of their defense against all invading microbes was poorly understood until now. By identifying the key Phlebiopsis gigantea genes and enzymes involved in resin metabolism, more effective biocontrol strains can be developed. This knowledge will also be valuable in advancing the industrial bioconversion of woody biomass into useful products, including bioenergy-related products.

Scanning electron micrograph of a radial section of pine wood with Phlebiopsis gigantea filaments visible during attack. Photo: Robert Blanchette and Benjamin Held, University of Minnesota.

Scanning electron micrograph of a radial section of pine wood with Phlebiopsis gigantea filaments visible during attack. Photo: Robert Blanchette and Benjamin Held, University of Minnesota.

FPL assistant director Ted Wegner observed that “This important body of research provides a fundamental science base for developing commercially viable and environmentally preferable ways of protecting conifers from root rot as well as opening the door for new commercially viable and environmentally preferable forest biomass conversion technologies.”

Within its genome of 30 million base pairs, Phlebiopsis gigantea was predicted to harbor 12,000 protein-encoding genes. The team of researchers identified specific genes involved in the degradation of pitch and novel enzymes produced by Phlebiopsis gigantea that could be of value in the industrial bioconversion of woody biomass. For example, utilization of freshly harvested conifer wood for bioconversion or for paper manufacture can be complicated by the resinous materials. The enzymes and enzymatic processes employed by Phlebiopsis gigantea may lead to the development of new approaches for the reduction or elimination of troublesome resins that interfere with pulping and papermaking processes and products. According to Cullen, “While commercial applications may be years away, the research findings offer considerable promise in reducing the costs of pitch deposits in paper manufacture.”

Regarding the economic importance of controlling Heterobasidion root disease, Professor Sarah Covert of the University of Georgia stated that “Heterobasidion root disease is one of the most costly conifer diseases in the entire Northern Hemisphere.”

The complete report can be found at http://www.plosgenetics.org/article/info%3Adoi%2F10.1371%2Fjournal.pgen.1004759

Wood Preservatives: New Report Explores Directions and Possibilities

A new report has just been published: Wood Protection Research Council, Research Priorities 2013

In this report, authors Carol A. Clausen, Frederick Green III, Grant T. Kirker, and Stan T. Lebow report on findings and recommendations from the Wood Protection Research Council.

Why wouldn’t a homeowner want to build with wood? Sometimes homeowners do not select wood as a building material because of its vulnerability to biodeterioration by fungi and insects under certain conditions of storage and use. These limitations are also a prime cause of user dissatisfaction. Therefore, efforts to protect wood from biological degradation are among the earliest research at the Forest Products Laboratory. This research has successfully reduced the demand for lumber from our National Forests by reducing the need to repeatedly replace existing wood products.

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The cycle of wood harvest, research, and use protects our natural resources.

Wood protection has undergone dynamic changes since the industry voluntarily withdrew chromated copper arsenate (CCA) from most residential uses and new products were introduced to the marketplace. According to the Environmental Protection Agency (EPA), “CCA is a chemical wood preservative containing chromium, copper and arsenic. CCA is used in pressure treated wood to protect wood from rotting due to insects and microbial agents. EPA has classified CCA as a restricted use product, for use only by certified pesticide applicators.”

Obviously, alternatives for wood protection are needed. However, to bring a new preservative to the marketplace, a considerable amount of performance data needs to be obtained. Current laboratory methodologies to determine the durability of test specimens are insufficient, and long-term field testing is required to ensure that a treatment is effective.

Improved accelerated test methods to predict performance would reduce the time needed for the development and acceptance of new preservatives. Potential improvements for accelerated testing may include selection of test fungi, techniques to detect incipient stages of fungal decay, methods to properly assess durability of wood plastic composites use of rapid laboratory bioassays for screening, and field tests that could measure loss in mechanical properties and statistical analysis.

Possibilities and research opportunities abound. For instance, protection systems could be targeted to specific problems. With nanotechnology at the forefront, novel advances in wood protection could replace the broad spectrum biocides traditionally used to inhibit decay fungi. The most logical approach to develop targeted biocides is to take advantage of unique physiological attributes of decay fungi, such as their ability to sequester metals through production of oxalic acid or natural tolerance to preservatives. Discerning and describing these mechanisms may enable us to design specific, targeted inhibitors to control decay and circumvent preservative tolerances that are common in brown-rot basidiomycetes.

This report summarizes presentations and comments from the inaugural Wood Protection Research Council meeting. Research needs for the wood protection industry were iden­tified and prioritized. Methods for successfully addressing research needs were discussed by industry, academia, and association representatives.