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Abstract
Phytophthora spp. occur widely in forest and other natural ecosystems. Because these straminipiles are well adapted to aquatic environments, monitoring strategically selected streams may reflect occurrence and distribution of
Phytophthora spp. over the relatively large area drained by these streams. The mountain region of western North Carolina, in the southern Appalachian Mountains, was designated as a high risk area for sudden oak death, caused by
P. ramorum, based on the occurrence of numerous native host plants, a relatively mild climate, and the prevalence of nursery businesses in this region that import plants or plant material from areas known to be infested. Therefore, five streams in three watersheds in Pisgah National Forest in western North Carolina were sampled monthly for
Phytophthora spp. from April 2005 to March 2006 to determine if
P. ramorum was present in the region, to determine the diversity of species of
Phytophthora native to the region, and to compare baiting and filtration as detection methods. For baiting, either four wounded or four nonwounded leaves of
Rhododendron maximum (a plant native to this region) were placed in a mesh bait bag made with nylon screen and PVC pipe (fig. 1). Wounded leaves were floated in a stream for 3 days while non-wounded leaves were exposed for 2 to 3 weeks. Water soaked lesions had developed on wounded leaves after 3 days in the water, and dark brown necrotic lesions were observed on non-wounded leaves exposed for 2 to 3 weeks. In the laboratory, five pieces of symptomatic leaf tissue were taken from each leaf, a total of 40 leaf pieces were embedded in PARPH-V8 selective medium to isolate
Phytophthora spp. for each stream. For filtration, one liter of water was collected from each stream, and samples were filtered within 10 hours of collection. Nine 100-ml subsamples of water were vacuum-filtered (fig. 2) through two types of membrane filters (47-mm in diameter) with three pore sizes (Nuclepore with 1- and 3-μm pores and Durapore with 5-μm pores), and filters were inverted on PARPHV8 medium to recover propagules of
Phytophthora spp. trapped on the filters (fig. 3).
Parent Publication
Citation
Hwang, Jaesoon; Oak, Steven W.; Jeffers, Steven. 2008. Detecting
Phytophthora ramorum and other species of
Phytophthora in Streams in natural ecosystems using baiting and filtration methods. In: Frankel, Susan J.; Kliejunas, John T.; Palmieri, Katharine M., tech. coords. 2008. Proceedings of the sudden oak death third science symposium. Gen. Tech. Rep. PSW-GTR-214. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. p. 4
