On the surface of a Douglas-fir needle, the spore of a fungal pathogen, Phaeocryptopus gaeumannii, germinates and sends forth threads (hyphae). It matures into an organism that will grow inside the needle and reproduce. By interfering with the tree’s ability to exchange air and water, it shuts down photosynthesis. Thus starts a disease known as Swiss needle cast, which causes more than $200 million in reduced Douglas-fir growth annually in Oregon.
Researchers in Oregon State’s Swiss Needle Cast Cooperative are studying the disease in order to develop treatments. Robin Rose, professor of forestry, used a scanning electron microscope to capture the fungus at work. The cross section of a needle, left, shows what appear to be hyphae among the needle’s cells, although it isn’t clear that the threads are from the pathogen. At right is an opening, or stomate, in the needle.
“I was looking for hyphae going into or out of the stomates of Douglas-fir needles,” says Rose.
A partnership with the Oregon Department of Forestry, USDA Forest Service and the forest industry, the cooperative was founded in 1997 to maintain productivity in the region’s Douglas-fir forests.