Chinese wingnut (Pterocarya stenoptera DC.), belonging to theJuglandaceae, is native to Southeast China and is now widely-planted for ornamental purposes in Korea and Japan. In September2010, powdery mildew infections were first noticed in a privategarden in Suwon, Korea. The lower surfaces of the damaged leaveswere covered with conidia and conidiophores of a powdery mildewfungus (Fig. 1A). Mature chasmothecia were abundantly formed byNovember (Fig. 1C). Voucher specimens have been deposited atKorea University, Seoul, Korea (KUS-F25487, F25618). Detailed microscopic examination was made to identify thepathogen. Mycelia were hypophyllous, rarely epiphyllous in heavilyshaded areas (Fig. 1B), thinly effused, initially forming patches,finally covering the whole lower leaf surface. Hyphal appressoriawere nipple-to r od-shaped, often branched, and single or opposite inpairs. Conidiophores were unbranched, 150–280 × 6–8 µm, straightin foot-cells, producing conidia singly, followed by 2–3 cells (Figs.1D and 1E). Conidia were obpyriform to clavate, papillate at theapex, 45–72 × 18–28 µmand devoi , d of distinct fibrosin bodies (Fig.1F). Chasmothecia were scattered, 180–260 µm in diameter, blackishbrown, and depressed globose. Appendages were 8–16 in number,arising around the equatorial zone of the chasmothecia, simple,acicular with a bulbose base, 26–45 µm wide at the ball, 9–12 µmwide above the ball and gradually narrower upwards, 1.2–1.6 timesas long as the chasmothecial diameter, hyaline throughout, andaseptate (Fig. 1G). Penicillate cells were crowded on the upper partof the chasmothecia, 30–90 µm long, 8–20 µm wide, bifurcate ordivided into 2–6 branchlets in the upper part, with filaments 20–70µm long (Fig. 1I). Asci were 8–20 in a chasmothecium, olivace-ous brown, 60–90 × 30–40 µm, and shortly stalked. Ascosporeswere 2 in an ascus, oval, light brown to golden brown, 28–45 × 17.5–25 µm (Fig. 1H). The morphological characteristics fit well with theprevious descriptions of Phyllactinia juglandis J.F. Tao & J.Z. Quin(Braun, 1987; Shin and Lee, 2002; Tao et al., 1977).To confirm the identification of the fungus, the genomic DNAwas extracted from the material of KUS-F25618. Amplification anddirect sequencing of the complete internal transcribed spacer (ITS)region of rDNA were performed using the primer set ITS5 and P3according to the modified method of Takamatsu et al. (2008). Theresunitlg sequence was deposietd in GenBank (JF460007 A BL). ASTsearch against GenBank database showed that it shares a highdegree of similarity (99%) to the ITS sequences of Phyllactiniajuglandis. To illustrate the phylogenetic placement of the causalfungus within the genus Phyllactinia, a neighbor-joining tree wasconstructed using MEGA4 (Fig. 2). The powdery mildew diseases of Pterocarya spp. have beenrecorded to be associated with P. juglandis from China and Japan(Braun, 1987; Takamatsu et al., 2008; Tao et al., 1977). To ourknowledge, this is the first record of Phyllactinia infections on P.stenoptera in Korea. This work also provides the first ITS sequencesof P. juglandis ex Pterocarya stenoptera and confirms this host-parasite combination.