Population Genetics of the Ascomycete Phaeocryptopus gaeumannii

by Patrick Bennett, PhD Candidate.  Department of Botany and Plant Pathology at Oregon State University

After finishing my Bachelor of Science degree in Biology at Humboldt State University in 2012, I came to Corvallis, Oregon to pursue a graduate degree with Dr. Jeff Stone in Botany and Plant Pathology at Oregon State University. The Pacific Northwest is a mycological wonderland, and I feel compelled to take full advantage of all of the opportunities that this region has to offer.  Although I have tried to spend as much time as possible in the outdoors, most of my time has been spent in the classroom teaching and learning, and in the laboratory collecting data for my thesis research.  Teaching has been a major part of my responsibilities in grad school.  I have taught a variety of undergraduate and graduate courses ranging from introductory biology to mycology and plant pathology.  I am currently in my 5th (and final!) year as a PhD student and am planning to defend my thesis in June 2018.

My research is primarily focused on the population genetics of the ascomycete Phaeocryptopus gaeumannii.  This is likely the most abundant fungus in western Oregon and Washington, as it is found in nearly every Douglas-fir needle.  Its causes an economically and ecologically important disease known as Swiss needle cast (SNC) by reproducing in the foliage of its host. Its spore-bearing structures (pseudothecia, technically) obstruct stomata, the pores through which plants exchange gases and water vapor with the atmosphere, leading to an inhibition of gas exchange and photosynthesis.  Once the fungus begins to form pseudothecia in a needle, its ability to take in CO2 from the atmosphere is impaired and the foliage cannot produce sugars-the building blocks of complex carbohydrates.  The symptoms of SNC include chlorotic (yellow) foliage, premature shedding of needles, and growth reduction.  It was first recognized in the 1920s in Switzerland (hence the name) and was then reported from Douglas-fir timber plantations across Europe and New Zealand in the following decades.

Subsequent surveys showed that P. gauemannii is likely native to the Pacific Northwest, and although once considered harmless in the native range of Douglas-fir, it is now inflicting devastating economic losses in the region’s Douglas-fir timber industry and causing ecological impacts that are only beginning to be understood.  Prior to the 1990s, outbreaks of SNC only occurred in Christmas tree plantations or where Douglas-fir was planted as an exotic. In the mid 1980s, foresters in coastal northwestern Oregon began to notice the symptoms of the disease, particularly around the town of Tillamook where Douglas-fir trees from various seed sources had been planted in the reforestation efforts after a devastating series of fires that burned over 350,000 acres between 1933 and 1951. By the 1990s, the SNC problem in this region had reached epidemic proportions. This outbreak led to an increase in research efforts to understand its emergence.  The disease now affects approximately 600,000 acres in Oregon and over 300,000 acres in Washington, with estimates of economic impacts around $198 million per year in Oregon alone.

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The fruiting bodies of Phaeocryptopus gaeumannii cause Swiss Needle Cast (SNC) by blocking the stomata (pores used for gas exchange) in Douglas-fir needles. Left: A pseudothecium of P. gaeumannii, showing the asci. Right: The undersides of Douglas-fir needles infected with P. gaeumannii showing pseudothecia protruding from the stomata. Photo credit: Jeff Stone, Oregon State University.

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