J. W. Zanzot1, J. L. Parke2, and E. M. Hansen2
In contrast to the situation in California where disease is widespread, Sudden Oak Death (SOD) is restricted to a small geographic area in Oregon. As eradication efforts progress, the potential effects on surrounding plant communities remains a contingency to be addressed.
The southwestern corner of Oregon, where SOD has been found, is adjacent to the Siskiyou Mountains, which harbor some of the most diverse plant communities in North America. Tanoak, the principal host for SOD in Oregon, is found throughout many of these communities, on the western side of the range. To better predict the disease risk to plant communities in this region, we are employing an USFS classification scheme in which 17 tanoak associations are defined by species presence and correlated with temperature and precipitation. We are using a detached leaf assay to identify potential foliar hosts among tree, shrub, and herb species in each of these tanoak associations.
Leaves are dipped in a suspension of P. ramorum zoospores and incubated in a moist chamber for seven days. The area of necrotic leaf tissue is determined, and compared to symptoms on leaves of known hosts. Previous work supports the validity of the detached leaf assay as an indicator of whole plant susceptibility (Parke, Linderman, and Hansen, 2002).
Many plant species associated with tanoak not yet exposed to the pathogen in nature appear susceptible to foliar necrosis by P. ramorum. This includes the understory species Chimaphila umbellata (common prince’s pine), Vaccinium parvifolium (red huckleberry) and Linnaea borealis (twinflower).
Understanding the potential susceptibility of tanoak associates to P. ramorum is a first step in predicting which plant communities in southwestern Oregon could be at greatest risk should the disease spread, and may help to inform the decision-making process.
