First Report of the Pear Trellis Rust Fungus, Gymnosporangium sabinae, on Pyrus calleryana ('Bradford' and 'Chanticleer') and P. communis in New York State

Owing to their relative disease resistance and showy spring flowers, cultivars of Callery pear (Pyrus calleryana) are commonly planted ornamental and streetside trees in New York state and elsewhere in the U.S. Over the past 2 years, we collected a leaf rust on P. calleryana 'Bradford' or 'Chanticleer' (also known as 'Cleveland Select') from Hempstead (Nassau County), East Moriches and Riverhead (Suffolk Co.), Rochester (Monroe Co.), and Staten Island (Richmond Co.), NY. Leaf samples were collected in June and August 2010 and 2011; adaxial surface lesions resembled infection by fungi in the genus Gymnosporangium (Pucciniales). Lesions were yellow- to red-orange with irregular red to purple margins, 1 to 3.5 cm in any one dimension, and contained 20 to 45 black, subepidermal spermogonia. Hypertrophied plant tissue was evident on the abaxial surface below the spermagonia, but aecia were absent. Genomic DNA was extracted from rust-infected tissue on P. calleryana 'Bradford' (East Moriches, Hempstead, Rochester, and Staten Island) and 'Chanticleer' (Riverhead), and the D1/D2 domain of the 28s ribosomal DNA was PCR-amplified using primers 4 and 11 (3) and sequenced. Partial 28s rDNA sequences (GenBank Accession Nos. JN969962 to JN969966) were either identical or nearly so (99%) to that of the trellis rust fungus, G. sabinae (AF426209 and AY512845). G. sabinae produces aecia with conspicuous balanoid peridia from August to November or until leaf drop; both characteristics are unique to the genus (1). We therefore monitored rust-infected Callery pears in Riverhead as well as a common pear (P. communis) in Ithaca, NY, for the appearance of aecia in 2011. The telial state of G. sabinae on taxa in the genus Juniperus sect. Sabina (e.g., J. sabina and J. virginiana) was not observed within the vicinity of affected pears. In late September, aecia of G. sabinae with morphological features identical to those described by Kerns (1) and Yun et al. (4) were collected from a P. calleryana in Riverhead (Cornell Plant Pathology Herbarium; CUP-067943) and a P. communis in Ithaca (CUP-067943): aecia roestelioid, hypophyllous; periderium balanoid, apex intact and conic, cancellate along the sides; aeciospores brown, globoid to broadly ellipsoid, 22.5 to 28.2 × 25.1 to 32.4 μm, walls 3.3 to 4.7 μm thick. A native of Eurasia and North Africa, G. sabinae was first identified in North America on common pear in 1960 in British Columbia and California (2). Thereafter, the fungus was collected on Callery pear in northern Washington in 1988 and recently, in Michigan in 2009 (4). To our knowledge, this is the first report of G. sabinae on P. calleryana 'Bradford' and 'Chanticleer' as well as P. communis in New York and the new records represent a large (>800 km) eastward expansion of the distribution of the pathogen in the U.S. The geographic locations of affected trees described herein suggest that the trellis rust fungus is well-established across New York, and has spread undetected since its introduction. Given the widespread planting of Callery pear and occurrence of susceptible Juniperus spp. in urban landscapes of New York, G. sabinae has the potential to become a perennial problem where epidemiological conditions permit host alternation. References: (2) F. Kerns. A revised taxonomic account of Gymnosporangium, 1973. (4) A. McCain. Plant Dis. Rep. 45:151, 1961. (1) G. Van der Auwera et al. FEBS Lett. 338:133, 1994. (3) H. Yun et al. Plant Dis. 93:841, 2009.

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

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.