Occurrence of Podosphaera pannosa Teleomorph on Rosa rugosa from Korea

Abstract

Rugosa rose ( Rosa rugosa Thunb.), also known as Japanese rose orbeach rose, is native to eastern Asia and southeastern Siberia, whereit grows on the coast, often on sand dunes. Various varieties havebeen widely introduced in Europe and North America forornamental purposes, particularly in coastal landscaping due to itsexcellent salt-tolerance. The plant is becoming common in Korea. Rust and powdery mildew have been described on this plant inKorea (The Korean Society of Plant Pathology, 2009). Only theanamorphic state of Podosphaera pannosa was recorded aspowdery mildew on R. rugosa in Korea (Shin, 1999). In September2009, formation of chasmothecia of P. pannosa was found on theleaves of R. rugosa planted in a hobby garden in Suwon, Korea(Fig. 1A). This finding was rather surprising, because there hadbeen only one case report of chasmothecia of P. pannosa from Rosadavurica in Asia (Shin, 1999). Voucher specimens accommodatingchasmothecia were housed at Korea University, Seoul, Korea(KUS-F24690, 24784, 25656).Chasmothecia were partly immersed in the mycelial layer, andwere amphigenous, but mostly hypophyllous, scattered or partlygregarious, 75–100 µm in diameter, and dark brown (Fig. 1B).Appendages were produced from the lower half of the chasmo-thecia. The appendages were mycelioid, uniformin width (4–6 µm),variable in length up to 4 times the diameter of the chasmothecia, 1–3-septate, brown at the base and becoming paler along their length.There was one ascus per chasmothecium (Fig. 1C). Asci were 80–100 × 60–80 µm, sometimes swelled in water, and oval to fusiform.Ascospores numbered eight per ascus and were ellipsoidal, 24–30 ×16–20 µm, and hyaline to pale yellowish due to numerous small oildrops (Fig. 1D). These data agreed with previous records of P.pannosa (Wallr.) de Bary (Braun, 1987; Shin, 1999).To confirm the identification, the complete internal transcribedspacer (ITS) regions of rDNA from KUS-F24784 were amplifiedwith the primers ITS5 and P3 (Takamatsu et al., 2009) andsequenced. The resulting sequences of 477 bp were deposited inGenBank (Accession number HQ852205). Phylogenetic analysiswas performed using MEGA4 with neighbor-joining method( usingTajima-Nei distances). The Korean isolate showed > 98% sequencesimilarities to AF011322 (468/477 bp), AB022348 (470/477 bp),and AB525937 (473/477 bp) of P. pannosa found on Rosa spp. (Fig.2). Therefore, the sequence analysis verified the chasmothecia on R.rugosa in Korea to be P. pannosa .Since the first description of the teleomorph of this species in1819, there have been several additional records on the rareoccurrence of chasmothecia in North America and Europe (cf.Braun, 1987). However, this is the first record of the occurrence of P.pannosa chasmothecia on R. rugosa globally and the second recordon a Rosa spp. in Asia. The role of chasmothecia in the severity ofpowdery mildew is still unknown. Most of the powdery mildewfungi are heterothallic (Braun, 1987); an unequal distribution ofmating types may partly explain the rare occurrence of chasmothecia.