TRACKING A TREE-KILLER: IMPROVING DETECTION AND CHARACTERIZING SPECIES DISTRIBUTION OF PHYTOPHTHORA CINNAMOMI IN APPALACHIAN FORESTS

Phytophthora cinnamomi is a soil-borne oomycete pathogen causing root rot in susceptible host species. P. cinnamomi is thought to have originated in Southeast Asia, but has since been introduced to many regions around the world, where it causes dramatic declines in many forest tree species. In the eastern US, the primary susceptible tree species of concern are American chestnut (Castanea dentata), white oak (Quercus alba), and shortleaf pine (Pinus echinata). American chestnut, functionally eliminated in the early 1900s by the rapidly acting chestnut blight (Cryphonectria parasitica), has been the subject of decades-long breeding efforts aimed at improving chestnut resistance to chestnut blight. To improve chestnut restoration success, and restoration of other susceptible species, the distribution patterns of P. cinnamomi on a landscape scale must be better understood. This project was initiated to develop an improved method for detecting P. cinnamomi to permit high-throughput screening of forest soils, and to implement the improved detection approach in characterizing the distribution patterns of P. cinnamomi in developing soils on reclaimed surface mines in eastern Kentucky, as well as mature forest soils within an undisturbed watershed in a reference-quality eastern Kentucky forest. We developed an improved detection method using a molecular DNA-amplification approach (PCR), which demonstrated similar sensitivity to traditional culture-based methods, but required less time and space than traditional methods. We used this detection approach to screen soils from a chronosequence of reclaimed surface mines (reclaimed at different points in time) to evaluate whether reclaimed surface mined sites become favorable for P. cinnamomi colonization over time. Our analysis detected P. cinnamomi at the two older sites (reclaimed in 1997 and 2003), but we did not detect P. cinnamomi at the two newer sites sampled (reclaimed in 2005 and 2007). These results suggest that surface mined sites become favorable for P. cinnamomi colonization over time, and should not be considered permanently “Phytophthora-free.” We also collected ~200 samples from a watershed in UK’s Robinson Forest, from plots representing a gradient of topographic position, slope, and aspect. This survey indicated that P. cinnamomi distribution in forests is complex and can be difficult to predict; however, P. cinnamomi was detected in both drier upslope sites and in moister drainage sites.