First Report of Powdery Mildew Caused by Erysiphe betae on the Invasive Weed Dysphania ambrosioides in Korea
Authors: Park M. J. , Cho S. E. , Wolcan S. , Shin H. D. 
Published: January 2012

Dysphania ambrosioides (L.) Mosyakin & Clemants (formerly Chenopodium ambrosioides L.), commonly known as epazote, is an herb that is native to Central America, South America, and southern Mexico. As well as in its native areas, it is used as an herb, tea, and food commodity in warm temperate to subtropical areas of Europe, the United States, and Asia. In Korea, however, this plant was accidentally introduced around the 1970s and has become widely naturalized by replacing indigenous plants and disrupting native ecosystems (3). Since 2006, powdery mildew infections of epazote have been consistently found in the southern part of Korea, including Jeju Island. Specimens (n = 8) have been deposited in the Korea University Herbarium (KUS). White mycelial and conidial growth was present mostly on leaf surfaces with sparse growth on young stems and inflorescences. Severely infected leaves were malformed. Slight purplish discoloration was present on the leaves contiguous with colony growth. Mycelial colonies were conspicuous, amphigenous, and epiphytic. Appressoria on the mycelia were lobed. Conidiophores were 110 to 200 μm long and produced conidia singly. Conidia were hyaline, oblong-elliptical, measured 30 to 48 × 13 to 18 μm, lacked fibrosin bodies, and produced germ tubes on the subterminal position. Chasmothecia were amphigenous, scattered or partly clustered, dark brown, spherical, 110 to 130 μm in diameter, and contained four to seven asci. Appendages were mycelioid, numbered 50 to 80 per chasmothecium, 0.5 to 1.5 times as long as the chasmothecial diameter, one- to three-septate, and brown at the base while becoming paler toward the tip. Asci were short stalked, 60 to 75 × 30 to 38 μm, and contained three to five spores. Ascospores were ellipsoid-ovoid with dimensions of 20 to 28 × 14 to 18 μm. On the basis of these morphological features, this fungus was identified as Erysiphe betae (Vanha) Weltzien (1). To confirm the identification, the complete internal transcribed spacer (ITS) region of rDNA from KUS-F23213 was amplified with primers ITS5 and P3 and sequenced (4). The resulting sequence of 560 bp was deposited in GenBank (Accession No. JQ041419). A GenBank BLAST search with the current data showed >99% (558 of 560 bp) similarity with the results for E. betae ex Beta vulgaris (sugar beet). Therefore, the sequence analysis verified the pathogen to be E. betae. Previous epazote infections by E. betae have been recorded in Argentina, Mexico, Romania, India, and Japan (1,2). In Taiwan, an epazote powdery mildew associated with Oidium erysiphoides f. sp. chenopodii J.M. Yen, an anamorph of E. betae, was recorded (1,2). To our knowledge, this is the first record of E. betae on epazote in Korea, and the first confirmation of epazote powdery mildew being identified as E. betae on the basis of holomorphic characteristics and ITS rDNA sequences. Our field observation suggests that the powdery mildew is acting as one of several limiting factors to suppress the expansion of this invasive weed in Korea.

References: (1) U. Braun. Beih. Nova Hedw. 89:1, 1987. (2) D. F. Farr and A. Y. Rossman. Fungal Databases. Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/ , November 22, 2011. (3) C. G. Song and Y. H. Yang. The Naturalized Plants in Jeju Island. Nam-Jeju County, Jeju, Korea, 2005. (4) S. Takamatsu et al. Mycol. Res. 113:117, 2009.