|Use of nested PCR to detect Ceratocystis fagacearum in sapwood of diseased northern oak species|
A. YANG (1), J. Juzwik (2), D. Mollov (3). (1) Department of Plant Pathology, University of Minnesota, St. Paul, MN, U.S.A.; (2) Northern Research Station, US Forest Service, St. Paul, MN, U.S.A.; (3) National Germplasm Resources Laboratory, USDA ARS, Beltsville, MD, U.S.A.
Early and accurate diagnosis of oak wilt, caused by <i>Ceratocystis fagacearum</i> (Cf), is important when disease control action is planned. When laboratory diagnosis is needed, standard isolation protocols that are used rely on high quality samples and require > 14 days for incubation. Use of a nested PCR protocol to detect Cf in diseased sapwood shavings was compared to detection success using published isolation methods. Assays were performed on samples from oak species common in the Lake States. Four subsamples of three branches collected from each tree were tested. In actively wilting red oaks, 97% of the subsamples from nine trees were positive for Cf using PCR compared to 82% using isolation techniques. For wilting branches from eight bur oaks, 92% of subsamples were positive for Cf versus 67% based on isolation. In eight white oaks, 93% of subsamples were positive for Cf using PCR compared to 47% with isolation. The fungus was not detected by either technique in subsamples of branches obtained from healthy oaks (controls). For bur and white oak branches dead for ≥ 1 year, Cf was detected using PCR (55 and 87% of subsamples, respectively), but was not detected by isolation. Similarly, only the PCR assay detected the pathogen in sapwood samples underlying remnant Cf sporulation mats on three main stem locations of seven trees. These findings are of particular interest to diagnostic laboratories that process disease-suspect samples in the region.