First Report of the Oak Wilt Fungus, Ceratocystis fagacearum, in New York State

Abstract

Ceratocystis fagacearum (T.W. Bretz) J. Hunt is considered to be the most destructive vascular pathogen of oaks (Fagaceae: Quercus spp.) in the eastern, north-central, and south-central United States. (1,2,4). All red oak species (subgenus Quercus: section Lobatae) are highly susceptible to C. fagacearum, and infected trees typically die within 3 months of first symptom expression. However, members of the white oak group (subgenus Quercus: section Quercus) are moderately to highly resistant to C. fagacearum and rarely die from oak wilt (1,3). In early August of 2008, we received branch samples taken from wilting red oaks (Q. rubra L.) growing in a residential neighborhood in Scotia, NY (Schenectady County). The endoconidial state of the oak wilt fungus, Thielaviopsis quercina (B.W. Henry) A.E. Paulin, T.C. Harr. & McNew, was consistently isolated from the xylem in the branches. The cultures were identified based on hyphal and conidial morphology on acidified potato dextrose agar (aPDA) as well as sequences of the internal transcribed spacer (ITS) (GenBank Accession No. FJ347031) and large subunit (LSU) (GenBank Accession No. FJ347030) regions of nuclear ribosomal DNA (rDNA). The nucleotide identities for the ITS and LSU sequences were a precise match, 99 and 100%, to rDNA sequences (GenBank Accession Nos. AF043598 and AF222483, respectively) of other isolates of C. fagacearum. According to the homeowners at the site, 12 red oaks have died during the last 3 years, and each tree died within one growing season after oak wilt-like symptoms were noted. In a brief survey of nearby properties in late August of 2008, we found 12 additional trees that were either expressing crown symptoms of oak wilt (e.g., premature leaf casting, bronzing of leaf margins, and water-soaked leaves) or were standing dead and within close proximity (5 to 10 m) to symptomatic trees. Branch samples from four of the symptomatic trees revealed limited (spotted) or no vascular discoloration; however, C. fagacearum was isolated from each suspect tree on aPDA. Remnants of gray mycelial mats and associated pressure cushions were observed beneath the bark of one standing dead oak. The sweet fruit-like odor characteristic of the oak wilt fungus was immediately evident once the bark overlying the mats was removed. Prior to this discovery, the Susquehanna River in north-central Pennsylvania was considered to be the northeastern limit for oak wilt occurrence in the United States (2,4). To our knowledge, this is the first report of the fungus from New York and expands the known range of C. fagacearum to the northeast by at least 300 km, supporting the hypothesis that the range of this fungus continues to expand via animal vectors and/or human activities (2). An isolate of C. fagacearum from New York has been deposited at the Centraalbureau voor Schimmelcultures (CBS 123913). References: (1) D. N. Appel. Ann. Rev. Phytopathol. 33:103, 1995. (2) J. Juzwik et al. Ann. Rev. Phytopathol. 46:13, 2008. (3) W. L. MacDonald et al. European oaks-susceptible to oak wilt? Page 131 in: Shade Tree Wilt Diseases. C. L. Ash, ed. The American Phytopathological Society, St. Paul, MN, 2001. (4) USDA Forest Service. Oak Wilt Distribution. Northeast Area, State and Private Forestry, St. Paul, MN. Online publication, 2005.

Challenges and Successes in Managing Oak Wilt in the United States

“…There are several communities in west Texas and the Upper Peninsula of Michigan, for example, where the oak wilt fungus was likely introduced on contaminated firewood. More direct evidence of firewood involvement was reported with the recent discovery of oak wilt in Schenectady Co., New York, where mat remnants were found on firewood (66). This same concern has been the focus of international attention where exportation of red oak timber from the eastern United States to Europe has been regulated (51,104).…”

“…The first report of oak wilt in New York (Schencctady Co.) in 2008 rcpre-.sents a northeastern extension of the previously known range of C. fagacearum by approximately 300 km (187 mi) (66). Since 2006, two additional counties in South Carolina have been reported with oak wilt, which represents expansion of the southeastern portion of the disease range (USDA Forest Service, Pest Event Database, as provided by D. Starkey.…”

“…Human-aided insect transmission also occurs. Because oak wilt mats may form on logs and firewood sawn from recently killed oaks, transport of such material can result in spread of the pathogen to previously oak wilt-free areas, such as most likely happened in infected counties in west Texas (6) and in New York (66). However, there is no evidence that C fagacearum is transmitted via nursery stock or seed (27).…”

“…The fungus can easily be identified in culture based on conidiophores and conidial morphology as well as the sweet odor produced when growing on acidified potato dextrose agar (12). Further confirmation may be obtained through sequencing of the intemal transcribed spacer (ITS) and large subunit regions of the nuclear ribosomal DNA (66). Presence of C. fagacearum in artificially inoculated wood sticks has been detected using a standard DNA extraction protocol followed by PCR using a nested protocol (standard ITSl and ITS4 primers and species-specific primers) (122).…”

Benchmarking a fast and simple on-site detection assay for the oak wilt pathogen Bretziella fagacearum

“…Currently, oak wilt disease is only found in Texas, midwestern and eastern states in the United States (USDA-Forest Service Northern Research Station, and Forest Health Protection, 2019), where it was potentially introduced many years ago (Juzwik et al, 2008). However, there has been a continuous northward spread of the disease, with an increasing number of infected counties being reported at the Canada-USA border (Jensen-Tracy et al, 2009).…”