First report of powdery mildew caused by erysiphe aquilegiae var. ranunculi on catharanthus roseus in Korea

Catharanthus roseus (L.) G. Don [Apocynaceae], known as Madagascar periwinkle, is popularly planted in gardens and parks for ornamental purposes globally. In September 2015, individuals of pot-grown C. roseus were found infected with a powdery mildew in a nursery in Seoul, Korea. Numerous chasmothecia were formed on the lesions by November. Two voucher specimens were deposited in the Korea University Herbarium (KUS-F29106 and F29108). The hyphal appressoria were well-developed, multilobed or moderately lobed, and positioned singly or in opposite pairs. Conidiophores were straight, 80 to 140 × 7 to 9 µm, and composed of 3 to 4 cells. Foot-cells of conidiophores were straight or slightly sinuous at the base and 40 to 70 µm long. Singly produced conidia were oblong-elliptical, 34 to 55 × 15 to 20 µm with a length/width ratio of 1.6 to 2.6, devoid of distinct fibrosin bodies, and showed angular/rectangular wrinkling of outer walls. Germ tubes were produced in the perihilar position of the conidia. Chasmothecia were amphigenous, 85 to 120 μm in diameter, and contained 4 to 7 asci. Peridium cells of chasmothecia were irregularly polygonal and 15 to 25 µm wide. Appendages were mycelioid, 1- to 4-septate, brown at the base and becoming paler. Asci were ellipsoid to obovoid, short stalked, and 45 to 60 × 30 to 40 μm. Ascospores numbered 3 to 5 were ellipsoidal, 20 to 25 × 11 to 14 μm. The morphological characteristics were consistent with previous records of Erysiphe aquilegiae var. ranunculi (Grev.) R.Y. Zheng & G.Q. Chen (Braun and Cook 2012). To confirm the identification, the complete internal transcribed spacer (ITS) regions of KUS-F29106 were amplified with primers ITS1/ITS4, and sequenced directly. The resulting 684-bp sequence was deposited in GenBank (accession no. KX979915). A GenBank BLAST search of the Korean isolate showed >99% similarity with E. aquilegiae var. ranunculi (e.g., AB015929, AF154322). Pathogenicity was confirmed through inoculation tests by pressing a diseased leaf onto young leaves of three asymptomatic, potted plants. Three noninoculated plants were used as controls. Plants were maintained in a greenhouse at 24 to 30°C. Inoculated leaves developed symptoms after 5 days, whereas the controls remained symptomless. The fungus on the inoculated leaves was identical morphologically to that observed on the original diseased leaves. Powdery mildews of C. roseus have been recorded as Leveillula taurica, Oidium sp., and Erysiphe sp. (Amano 1986; Watanabe and Sato 2009; Farr and Rossman 2016). Liberato and Cunnington (2006) reported E. aquilegiae as a powdery mildew of C. roseus, and Braun and Cook (2012) listed the fungus as E. aquilegiae var. ranunculi. To our knowledge, this is the first report of powdery mildew caused by E. aquilegiae var. ranunculi on C. roseus in Korea. Since infected, symptomatic plants may cause loss in sale of nursery plants and market value, control strategies should be followed.