Taxonomy, Phylogeny, and Host Expansion of Powdery Mildew Fungi Parasitic to Veronica Species.

Powdery mildew is a prevalent fungal disease that affects various Veronica spp. (Plantaginaceae), caused by species in the genera Podosphaera and Golovinomyces (Erysiphales). There have been recent taxonomic changes in these groups and ongoing disease occurrence on a range of Veronica species previously unrecognized as hosts; however, the pathogen found in Korea remains unidentified. This study aimed to identify the causative agent of powdery mildew on Veronica spp. in Korea through molecular phylogenetic analysis of internal transcribed spacer (ITS) and large subunit (LSU) sequences of rDNA and morphological examination. Our study identified Golovinomyces bolayi as the sole pathogen affecting all nine Veronica species in Korea and confirmed that G. cichoracearum s. str., which was previously identified as the pathogen, was not the causal agent. These results expand the known host range of G. bolayi, including the addition of five Veronica species in Korea: V. hederifolia, V. kiusiana var. glabrifolia, V. longifolia, V. polita, and V. serpyllifolia. Notably, V. kiusiana has been added as a new global host of powdery mildew. These findings substantially enhance our understanding of the taxonomy of powdery mildew pathogens on Veronica species and provide valuable insights into their evolutionary host expansion.

First Report of Anthracnose Caused by Colletotrichum spaethianum on Hosta longipes in Korea.

Hosta longipes (Franch. & Sav.) Matsum. (Asparagaceae) is a perennial, herbaceous plant, native to Japan and Korea (Lee et al. 2021). In Korea, the plant is used as an edible vegetable and ornamental (Kang and Ju 2015). During 2021-2022, anthracnose symptoms were observed on leaves of H. longipes with over 70% disease incidence in Wanju-gun (35°38'47''N; 127°31'16''E) and Jangsu-gun (35°35'31''N; 127°30'03''E) in Jeollabuk-do, Korea. The disease initially appeared on old leaves, gradually spreading to young ones. The symptoms were characterized as yellow to white discoloration on the upper leaf surface with black necrotic tissue in the center of the lesion. Three H. longipes samples with anthracnose symptoms were collected. From each, a monoconidial isolate was obtained and then deposited in the Korea Agricultural Culture Collection (accession Nos. KACC 410038, 410391, and 410443). The dried specimens were housed at the herbarium of Jeonbuk National University (JBNU0129, 0137) and Korea University (KUS-F33379). Conidiomata was acervular, 65 to 80 × 56 to 70 µm in diam. Setae were dark brown, 2 to 4-septate, 63 to 161 µm long, being formed on a pale brown cushion. Conidia were hyaline, smooth-walled, aseptate, slightly curved, base truncate, 3.9 to 5.1 × 17 to 23 µm. The appressoria were solitary, olivaceous-brown, ovoid or irregularly shaped. Two-week-old colonies grown on PDA at 25 ℃ were 20-25 mm in diameter, initially white, then turned gray with age, with cottony aerial mycelium. The morphological and cultural characteristics of the fungus were consistent with those of Colletotrichum spaethianum (Allesch.) Damm, P.F. Cannon & Crous (Damm et al. 2012). To confirm morphology-based identification, the nucleotide sequences of the internal transcribed spacer (ITS) rDNA region, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), actin (actA), chitin synthase (CHS1), histone (HIS3) and tubulin (TUB2) genes were determined for KACC410443, as outlined by Cannon et al. (2012) and Damm et al. (2009). The resulting sequences were submitted into GenBank (PP000829 for ITS, PP133094 for GAPDH, PP083418 for actA, PP133091 for CHS1, PP133097 for HIS3, and PP133099 for TUB2) and compared with reference sequences in GenBank using BLASTn search tool. The results showed a 100% match with C. spaethianum (MT611068), C. incanum (MN880260) and C. truncatum (EF016303) for ITS, and 100% with C. spaethianum for GAPDH (MH370513), actA (MH045677), CHS1 (MH370520), HIS3 (MH985161), and TUB (MH456884). Pathogenicity was tested by inoculating conidial suspension (1 ×104 cfu/ml) of three-week-old fungal colonies of the isolate KACC410443 onto leaves of three healthy potted plants. Prior to inoculation, leaves were deliberately wounded by pinpricking with a sterilized needle. Two wounded but non-inoculated plants served as controls. Plants were maintained in a greenhouse at 25 to 30 °C. Inoculated plants developed anthracnose symptoms after eight days, while the control plants remained symptomless. The fungus isolated from the inoculated plants was morphologically identical to that observed initially, fulfilling Koch's postulates. To our knowledge, there is no previous record of C. spaethianum on H. longipes, although C. spaethianum has been reported to infect another species, H. plantaginea (Cheon and Jeon 2016). This is the first report of this fungus on H. longipes in Korea (KSPP 2024) and globally (Farr and Rossman 2024). The anthracnose on this ornamental plant can be considered a new severe threat to planting strategies in gardens.

Unraveling the Life Cycle of Nyssopsora cedrelae: A Study of Rust Diseases on Aralia elata and Toona sinensis.

Rust disease poses a major threat to global agriculture and forestry. It is caused by types of Pucciniales, which often require alternate hosts for their life cycles. Nyssopsora cedrelae was previously identified as a rust pathogen on Toona sinensis in East and Southeast Asia. Although this species had been reported to be autoecious, completing its life cycle solely on T. sinensis, we hypothesized that it has a heteroecious life cycle, requiring an alternate host, since the spermogonial and aecial stages on Aralia elata, a plant native to East Asia, are frequently observed around the same area where N. cedrelae causes rust disease on T. sinensis. Upon collecting rust samples from both A. elata and T. sinensis, we confirmed that the rust species from both tree species exhibited matching internal transcribed spacer (ITS), large subunit (LSU) rDNA, and cytochrome oxidase subunit III (CO3) mtDNA sequences. Through cross-inoculations, we verified that aeciospores from A. elata produced a uredinial stage on T. sinensis. This study is the first report to clarify A. elata as an alternate host for N. cedrelae, thus providing initial evidence that the Nyssopsora species exhibits a heteroecious life cycle.

First Report of Powdery Mildew Caused by Golovinomyces adenophorae on Adenophora triphylla var. japonica in Korea.

Adenophora triphylla var. japonica (Campanulaceae), known as Japanese lady bell, is native to East Asia. It has been used as a medicinal plant but is widely cultivated in Korea as an indigenous vegetable (Park et al. 2011). In the summer of 2020, about 100 plants in an experimental plot at the National Institute of Forest Science, Seoul, Korea, showed powdery mildew symptoms with a 100% disease incidence. Signs first appeared as white colonies, subsequently expanding over the leaves, stems, and inflorescences. Infected young shoots were elongated and became slender. Chasmothecia were found in late October. Voucher specimens were deposited in the Korea University Herbarium (KUS-F). Conidiophores arising from the lateral part of the hyphae were upright, 100 to 220 × 10 to 12 µm, and produced 2 to 5 immature conidia in chains with sinuate edge lines. Basal parts of foot-cells in conidiophores were curved. Conidia were barrel-shaped to ellipsoid, 26 to 40 × 14 to 20 µm, and produced germ tubes on the perihilar position of the conidia. Chasmothecia with short mycelioid appendages were gregarious, 144 to176 µm in diam., and contained 8 to 22 asci. Asci were clavate-saccate with short stalks, 60 to 82 × 28 to 42 µm, and contained two spores. Ascospores were broadly ellipsoid, cytoplasm-dense without vacuoles, colorless, and 22 to 28 × 12 to 18 µm. The structures and measurements were consistent with those of Golovinomyces adenophorae (R.Y. Zheng & G.Q. Chen) Heluta (Braun & Cook, 2012). To confirm the morphology-based identification, two herbarium specimens (KUS-F29252 and F31898) were sequenced for the internal transcribed spacer (ITS) and large subunit (LSU) regions with PM10/ITS4 and PM3/TW14 primers, respectively (Bradshaw and Tobin, 2020). A Blastn search revealed high similarities in the ITS and LSU sequences, with 99.81% (538/539 bp) and 99.86% (697/698 bp) to G. adenophorae sequences (AB077633 and AB077632), respectively. All resulting sequences were deposited in GenBank under accession numbers OR841069-70 for ITS and OR841071 for LSU. A pathogenicity test was performed through inoculation by gently dusting the conidia from a detached symptomatic leaf onto the leaves of five healthy plants. Five non-inoculated plants served as controls. Following inoculation, plants were covered with plastic film and maintained in a greenhouse (24 to 32°C) until symptoms developed. Powdery mildew colonies developed on the inoculated plants after twelve days, whereas the control plants remained symptomless. The inoculated pathogen was confirmed morphologically and molecularly by the sequence comparison aforementioned, fulfilling Koch's postulates. Based on morphological characteristics and the sequencing data, the powdery mildew was identified as G. adenophorae. The association of G. adenophorae and Adenophora spp. has been known in China, Japan, Kazakhstan, and the Far East of Russia (Farr and Rossman, 2023). This is the first report of powdery mildew caused by G. adenophorae on A. triphylla var. japonica in Korea. Since the commercial cultivation of this plant aims to harvest young shoots as one of the most popular vegetables in Korea, appropriate control measures for the powdery mildew should be considered.

Re-identification of Colletotrichum gloeosporioides Species Complex Isolates in Korea and Their Host Plants.

The Colletotrichum gloeosporioides species complex includes many phytopathogenic species, causing anthracnose disease on a wide range of host plants and appearing to be globally distributed. Seventy-one Colletotrichum isolates in the complex from different plants and geographic regions in Korea were preserved in the Korean Agricultural Culture Collection (KACC). Most of them had been identified based on hosts and morphological features, this could lead to inaccurate species names. Therefore, the KACC isolates were re-identified using DNA sequence analyses of six loci, comprising internal transcribed spacer, gapdh, chs-1, his3, act, and tub2 in this study. Based on the combined phylogenetic analysis, KACC strains were assigned to 12 known species and three new species candidates. The detected species are C. siamense (n = 20), C. fructicola (n = 19), C. gloeosporioides (n = 9), C. aenigma (n = 5), C. camelliae (n = 3), C. temperatum (n = 3), C. musae (n = 2), C. theobromicola (n = 2), C. viniferum (n = 2), C. alatae (n = 1), C. jiangxiense (n = 1), and C. yulongense (n = 1). Of these, C. jiangxiense, C. temperatum, C. theobromicola and C. yulongense are unrecorded species in Korea. Host plant comparisons showed that 27 fungus-host associations are newly reported in the country. However, plant-fungus interactions need to be investigated by pathogenicity tests.

First Report of Powdery Mildew Caused by Golovinomyces ambrosiae on Xanthium orientale in Korea.

Xanthium orientale L. (syn. Xanthium canadense Mill., Asteraceae), known as cocklebur, is an annual weed native to North America, which is now a neophyte distributed throughout the world. This plant was accidentally introduced to Korea in the late 1970s ( So et al. 2008) and is considered a problematic exotic weed in orchards, for which many herbicides are ineffective (Kim et al. 2020). In September 2018, powdery mildew was observed on X. orientale in Jeju, Korea. The disease incidence ranged from 40 to 60%. Voucher specimens were deposited in the Korea University Herbarium (Accession No. KUS-F30795) and Kunsan National University Herbarium (KSNUH1988). Symptoms appeared as round to irregular white patches with abundant hyphal growth on the leaf surface. Hyphal appressoria were nipple-shaped, and 3 to 6 µm diam. Conidiophores (n = 30) were 145 to 206 × 9 to 11.6 µm and produced 2 to 5 immature conidia in chains with a sinuate outline. Foot-cells of the conidiophores were straight, cylindrical, and 43 to 100.9 µm long. Conidia (n = 30) were ellipsoid-ovoid, doliiform to somewhat limoniform, 25.2 to 31.8 × 13.6 to 16.8 µm (l/w 1.6 to 2.1), and devoid of distinct fibrosin bodies. The morphological characteristics corresponded to those of Golovinomyces ambrosiae (Schwein.) U. Braun & R.T.A. Cook (Braun and Cook 2012, under Golovinomyces spadiceus (Beck. & M.A. Curtis) U. Braun; Qiu et al. 2020). To confirm the identity of the causal fungus, the internal transcribed spacer (ITS), large subunit (LSU) (Bradshaw and Tobin 2020), the intergenic spacer (IGS) of rDNA, and the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene (Bradshaw et al. 2022) were amplified for a herbarium specimen (KUS-F30795). A BLASTn search of these sequences revealed 100% identity with reference sequences of G. ambrosiae on diverse Asteraceae plants (AB077644 for ITS, AB077643 for LSU, ON361171 for IGS, and ON075648 for GAPDH). However, there was a single nucleotide difference on both the IGS and GAPDH sequences when compared to the closely related species Golovinomyces latisporus. The sequences were deposited in GenBank (Accession No. OQ165157 (ITS), OQ165164 (LSU), OR050524 (IGS), and OR086076 (GAPDH)). Phylogenetic analyses of ITS, LSU, IGS, and GAPDH sequences revealed the Korean sample formed a well-supported group with other G. ambrosiae sequences, confirming its identity. A pathogenicity test was performed through inoculation by gently pressing diseased leaves onto the leaves of five healthy plants. Five non-inoculated plants served as controls. All plants were maintained in a greenhouse at 25±2°C. Powdery mildew colonies developed on the inoculated plants after ten days, whereas the control plants remained symptomless. The fungus present on the inoculated leaves was morphologically identical to that observed on the initially diseased leaves, fulfilling Koch's postulates. Powdery mildew on X. orientale has previously been reported as Golovinomyces cichoracearum (≡ Erysiphe cichoracearum) sensu lato in the USA, G. ambrosiae (= G. spadiceus) throughout all continents, and Podosphaera fusca sensu lato (now P. xanthii) in Korea (Braun and Cook 2012; Farr and Rossman 2023). To date, powdery mildew in Korea has been reported only on Xanthium strumarium as G. cichoracearum s. lat. and Podosphaera xanthii (KSPP 2022). To our knowledge, this is the first report of powdery mildew caused by G. ambrosiae on X. orientale in Korea.

Erysiphe lonicerigena sp. nov., a Powdery Mildew Species Found on Lonicera harae.

A powdery mildew (Erysiphaceae) has been continuously collected on the leaves of Lonicera harae in the southern part of the Korean Peninsula, where this shrub is indigenous. Microscopic examination of the asexual morphs revealed that the current collections are differentiated from the all known Erysiphe species on Lonicera spp. by its longer conidiophores and longer conidia. Although the morphology of the chasmothecia is reminiscent of Erysiphe ehrenbergii and E. lonicerae, the specimens on L. harae differ from them in having smaller ascospores. A phylogenetic tree generated from a combined dataset of the internal transcribed spacer region and 28S rDNA gene sequences demonstrates that sequences obtained from three powdery mildew collections on L. harae clustered together as an independent species clade with high bootstrap values distant from other Erysiphe species on Lonicera, representing a species of its own. Based on morphological differences and molecular-phylogenetic results, the powdery mildew on L. harae is proposed as a new species, Erysiphe lonicerigena, and the holomorph of the fungus is described and illustrated in this study.

First Report of Powdery Mildew Caused by Podosphaera xanthii on Verbena bonariensis in Korea.

Verbena bonariensis L. (Verbenaceae), known as purple-top vervain or Argentinian vervain, is a perennial, herbaceous plant, native to tropical South America. It is widely grown as an ornamental worldwide. During summer and autumn of 2022, V. bonariensis of an unknown cultivar with purple-violet flowers was found infected by powdery mildew fungus with 100% disease incidence in a public garden in Jeonju, Korea. White, superficial mycelia developed on infected plants and subsequently covered whole surfaces of leaves and stems, resulting in leaf discoloration and early defoliation. High disease severity caused poor growth of the plants, resulting in premature senescence and reduced flowering. A representative voucher specimen was submitted in the Korea University herbarium (KUS-F33160). Morphological characterization and measurements of the fungus were carried out using a fresh sample. Appressoria on the mycelium were poorly developed, nipple-shaped or nearly absent. Conidiophores were 90 to 246 × 10 to 12 µm and produced 2 to 7 immature conidia in chains with a crenate outline. Foot-cells of conidiophores were straight, cylindrical, relatively short, 42 to 64 µm long, and constricted at the branching point from the hypha. Conidia were hyaline, ellipsoid to ovate, measured 28 to 40 × 18 to 22 µm (length/width ratio of 1.4 to 2.0), and contained conspicuous fibrosin bodies. Germ tubes were produced from the lateral position of conidia. No chasmothecia were observed throughout the growingseason. These diagnostic structures were typical to the anamorph of the genus Podosphaera. The morphological characteristics and measurements were consistent with those of P. xanthii (Castagne) U. Braun & Shishkoff (Braun & Cook 2012). To confirm morphology-based identification, the nucleotide sequences of the internal transcribed specer region (ITS1 and ITS2) and large subunit gene (LSU) of the rDNA were determined in this study outlined by Bradshaw and Tobin (2020). The resulting sequences were submitted to GenBank (OQ061318 for ITS, OQ061319 for LSU) and were 100% identical with sequences of Podosphaera xanthii (MT242593, LC371331 etc.) for both ITS and LSU gene from the BLAST'n search results. Thus, based on morphology and results of molecular analysis, the isolate on V. bonariensis in Korea was identified as P. xanthii. The pathogenicity test was carried out by touching a diseased leaf onto healthy leaves of five pot-grown plants. Five non-inoculated plants were used as controls. After 7 days, typical powdery mildew colonies started to appear on the inoculated leaves. All control plants remained symptomless. The fungus isolated from the inoculated leaves was morphologically identical to that observed on the originally diseased leaves, which supports Koch's postulates. Hitherto, powdery mildew of Verbena spp. associated with Podosphaera sp. (including Sphaerotheca sp.) has been globally reported (Farr & Rossman 2022). Podosphaera xanthii on V. bonariensis was recorded from China and Japan (Hong et al. 2021, Farr & Rossman 2022), while in Korea, this fungus was recorded on Verbena brasiliensis (Cho et al. 2014), but not on V. bonariensis. To our knowledge, this is the first report of powdery mildew disease caused by P. xanthii on V. bonariensis in Korea. Our field observations suggest that this powdery mildew occurs on V. bonariensis planted in the shade. This finding could be useful for the breeding programme of Verbena spp. and for planting strategies in gardens.

First Report of Powdery Mildew Caused by Golovinomyces ambrosiae on Erigeron annuus in Korea.

Erigeron annuus (L.) Pers., known as annual fleabane or eastern daisy fleabane, is native to North America and was unintentionally introduced to Korea in the 1910s (Park, 1995). It is now widely naturalized throughout Korea and was designated as one of the ten major introduced plants in Korea by the Korea National Arboretum. In September 2012, several dozen annual fleabanes were found to be heavily infected with powdery mildew. Symptoms first appeared as circular to irregular white patches, which subsequently showed abundant hyphal growth on both sides of the leaves. The same symptoms have continuously been found on annual fleabane throughout the country, where the disease incidence was often higher than 80%. Five voucher specimens were deposited in the Korea University Herbarium (KUS-F30208, 31414, 31774, 31784 and 32003). Hyphae were septate, branched, and 4.5 to 6.7 µm wide. Appressoria on the mycelium were lobed. Conidiophores (n = 30), measured 154 to 215 × 9 to 12.5 µm, were simple and produced 2 to 4 immature conidia in chains with a sinuate outline, followed by 2 to 3 cells. Foot-cells of conidiophores were straight, cylindrical, and 40 to 98 µm long. Conidia (n = 30) were hyaline, ellipsoid to barrel-shaped, measured 25.3 to 35.8 × 13 to 17 µm (length/width ratio = 1.62 to 2.31), lacked distinct fibrosin bodies, and showed reticulate wrinkling of the outer walls. Primary conidia were apically rounded and basally truncated and generally smaller than the secondary conidia. Germ tubes were produced on the subterminal position of conidia. No chasmothecia were observed. The structures described above were typical of the Euoidium anamorph of the genus Golovinomyces, and the fungus measurements were compatible with those of G. ambrosiae (Schwein.) U. Braun & R.T.A. Cook (Qiu et al., 2020). To confirm the identity of the causal fungus, the internal transcribed spacer (ITS) and large subunit (LSU) regions of rDNA from the five herbarium specimens were amplified with primers PM10/ITS4 for ITS and PM3/TW14 for LSU (Bradshaw and Tobin, 2020; Mori et al., 2000; White et al., 1990) and sequenced directly. The resulting sequence was deposited in GenBank (Accession No. OP788040-4 for ITS and OP788045-9 for LSU). Comparison with the sequences available in the GenBank database revealed that the isolates showed 100% sequence similarity with those of G. ambrosiae from the family Asteraceae (e.g., MT355557, MF612182, etc.). Pathogenicity was confirmed through inoculation by gently pressing diseased leaves onto the leaves of five healthy potted plants. Five non-inoculated plants served as controls. Plants were maintained in a greenhouse at 22 to 28°C. Inoculated plants developed signs and symptoms after seven days, whereas the control plants remained healthy. The fungus present on the inoculated plants was morphologically identical to that observed initially on diseased plants, fulfilling Koch's postulates. Powdery mildew infections of Erigeron spp. associated with Golovinomyces species have been known in the United States, France, and China (Farr and Rossman, 2022). To our knowledge, this is the first report of powdery mildew disease caused by G. ambrosiae on E. annuus outside of North America as well as in Korea. According to our field observation, powdery mildew infections were found only on annual fleabanes growing in shady areas, not in sunny places.

First Report of Powdery Mildew Caused by Golovinomyces ambrosiae on Solanum carolinense in Korea.

Solanum carolinense L. (Solanaceae) is a perennial herbaceous plant native to the southeastern United States. The plant has been invasive in Europe, Australia, and Asia. It was accidentally introduced to Korea in the 1960s (Oh et al. 2002) and is now widely naturalized mostly in the southern area of the Korean peninsula. Since 2002, it has been designated as one of 'harmful non-indigenous plants' by the Korean Ministry of Environment due to its adverse effects on native plants. In September 2014, several S. carolinense plants were found infested with a powdery mildew disease in Busan, which was the first for Korea. Later in 2020-2022, hundreds of plants were continuously observed with an approximately 50% disease incidence in Jeonju, Korea. Symptoms first appeared as circular to irregular white patches, which subsequently coalesced to develop into abundant hyphal growth on both sides of the leaves. Representative voucher specimens were deposited in the Korea University herbarium (KUS-F28240 and F32541). Hyphal appressoria were nipple-shaped. Conidiophores were cylindrical, 110 to 190 × 10 to 12 µm, and produced 2 to 5 immature conidia in chains with a sinuate outline. Foot-cells of conidiophores were straight, cylindrical, and 58 to 90 µm long, followed by 2 to 3 cells. Conidia were ellipsoid to barrel-shaped, 29 to 36 × 15 to 20 µm (l/w 1.6 to 2.0), and devoid of distinct fibrosin bodies. Germ tubes were at the perihilar position of the conidia. Sexual stage was not developed. These morphological characteristics are consistent with those of Golovinomyces ambrosiae (Schwein.) U. Braun & R.T.A. (Braun and Cook 2012). Sequences of the internal transcribed spacer (ITS) region and large subunit (LSU) gene of rDNA were determined using primer pairs ITS1/PM6 and PM3/TW14, respectively (Bradshaw and Tobin 2020). A comparison of the resulting sequences using the BLASTn algorithm showed 100% identity with reference sequences of G. ambrosiae (MT355556, AB769425) and G. spadiceus (MN365027) for ITS and LSU in NCBI. Obtained sequences were deposited in GenBank (Accession Nos: OP585651-OP585654). A Maximum parsimony tree was constructed based on ITS+LSU dataset consisting of 23 sequences. Our sequences were clustered with sequences of G. ambrosiae, G. latisporus and G. cichoracearum, and supported with 100% BS value. A pathogenicity test was performed by gently dusting conidia onto leaves of five healthy potted plants. Five non-inoculated plants served as controls. Powdery mildew colonies developed on all inoculated plants after 5 days, whereas the control plants remained symptomless. The fungus present on the inoculated leaves was morphologically identical to that observed on the originally diseased leaves, which supports Koch's postulate. Previously, Erysiphe cichoracearum (syn. of G. cichoracearum) was recorded on this plant in theUSA (Farr and Rossman 2022). Since G. cichoracearum has been divided into several distinct species (Takamatsu et al. 2013, Qiu et al. 2020), the current taxonomic position of the North American isolate is unknown. In Korea, G. ambrosiae was reported on several asteraceous hosts such as Bellis perennis, Brachyscome multifida, Helianthus annuus, H. salicifolius, and Verbena bonariensis (Farr and Rossman 2022). To our knowledge, this is the first report of powdery mildew on this plant outside the USA. According to our field observations, powdery mildew infestation had little effect on plant growth and vigor.   References: Braun, U., and Cook, R. T. A. 2012. Taxonomic Manual of the Erysiphales (Powdery Mildews), CBS Biodiversity Series No. 11. CBS, Utrecht, Netherlands. Bradshaw, M., and Tobin, P.C. 2020. Phytopathology 110:1248. Farr, D. F., and Rossman, A. Y. Fungal Databases, Syst. Mycol. Microbiol. Lab., Online publication. ARS, USDA. Retrieved October 5, 2022. Oh, S. M., et al. 2002. Kor. J. Weed Sci. 22:280. Qiu, P-L., et al. 2020. BMC Microbiology 20:51. Takamatsu S., et al. 2013. Mycologia 105:1135.

First Report of Powdery Mildew Caused by Golovinomyces ambrosiae on New York Aster (Symphyotrichum novi-belgii) in Korea.

Symphyotrichum novi-belgii (L.) G.L. Nesom (syn. Aster novi-belgii L.), known as New York aster, is a perennial herb used in gardens and as a potted plant. The plant is native to North America but has been developed into various horticultural varieties. In Korea, it is one of the most common plants used for autumn bloom. In September 2011, New York asters (variety unknown) showing typical signs of powdery mildew were observed in a public garden in Seoul, Korea. Since then, the disease on New York asters has been continuously found in parks and flower markets in different regions of Korea. Voucher specimens (n=3) were deposited in the Korea University Herbarium (KUS-F 30752, 31865, and 32103). On leaves, circular to irregular white patches appeared which subsequently showed abundant hyphal growth on both sides of the leaves and on young stems and inflorescences, reducing the aesthetic value and vigor of the plants affected. Hyphae were septate, branched, and 4 to 8 µm wide. Appressoria on the mycelium were nipple-shaped. Conidiophores measured 110 to 200 × 9 to 11.5 µm, were simple, and produced 2 to 5 immature conidia in chains with a sinuate outline, followed by 2 to 3 cells. Foot-cells of conidiophores were straight, cylindric, and 55 to 125 µm long. Conidia were hyaline, ellipsoid to barrel-shaped, measured 22 to 52 × 15 to 20 µm (length/width ratio = 1.5-2.5), lacked distinct fibrosin bodies, and produced germ tubes on the subterminal position, with reticulate wrinkling of the outer walls. No chasmothecia were observed. The structures described above were typical of the Oidium subgenus Euoidium anamorph of the genus Golovinomyces, and the fungus measurements were consistent with those of G. ambrosiae (Schwein.) U. Braun & R.T.A. Cook (Braun and Cook 2012, Qiu et al. 2020). To confirm the identity of the causal fungus, the internal transcribed spacer (ITS) and large subunit (LSU) regions of rDNA were amplified with primers PM10/ITS4 for ITS and PM3/TW14 for LSU (Mori et al. 2000, Bradshaw and Tobin 2020). The resulting sequences were deposited in GenBank (Accession No. OP028065-7 for ITS and OP028053-5 for LSU). A GenBank BLAST search of these sequences revealed 100% identity with sequences of G. ambrosiae on many asteraceous plants, including S. novi-belgii from China (MK452575-9 for ITS and MK452648-52 for LSU). Pathogenicity was confirmed through inoculation by gently pressing diseased leaves onto leaves of five healthy potted New York aster plants. Five non-inoculated plants served as controls. Plants were maintained in an incubator at 24°C. Inoculated plants developed signs and symptoms after three weeks, whereas the control plants remained symptomless. The fungus present on the inoculated plants was morphologically identical to that observed initially on diseased plants, fulfilling Koch's postulates. The powdery mildew infections of S. novi-belgii associated with G. ambrosiae have been widely known in Europe and North America but only recently in China (Qiu et al. 2020, Farr and Rossman 2022). In Japan, Podosphaera fuliginea was known to be associated with powdery mildew of S. novi-belgii (Farr and Rossman 2022). To our knowledge, this is the first report of powdery mildew caused by G. ambrosiae on S. novi-belgii in Korea. The powdery mildew on this ornamental plant can be considered a severe threat.

First Report of Powdery Mildew Caused by Golovinomyces ambrosiae on Leucanthemum vulgare in Korea.

Leucanthemum vulgare Lam. (Asteraceae), known as ox-eye daisy, is a perennial herb native to Europe and western Asia (Clements et al. 2004, McDougall et al. 2018). In Korea, this plant was introduced for ornamental purposes but has been naturalized as a widespread invasive species. In June 2015, symptoms of a powdery mildew disease were observed on L. vulgare in a public garden in Goseong (38°14'18"N, 128°32'56"E), Korea. Since then, its findings have continued throughout the country, including Mokpo and Seogwipo (in 2018), Hongcheon and Seoul (in 2020), Boeun, Gunsan, and Namwon (in 2022), where the disease incidence was often higher than 80%. Symptoms first appeared as circular to irregular white powdery patches covering leaves and stems. Affected plants became distorted, eventually losing their aesthetic and ornamental value. A total of sixteen samples were deposited in the herbarium of Korea University (KUS-F), Korea. Microscopic observations showed that hyphal appressoria were nipple-shaped. Conidiophores were cylindrical, 98 to 157 × 9 to 12 µm, and produced 2 to 5 immature conidia in chains with a sinuate outline. Foot cells were cylindrical, straight, and 37 to 65 µm long. Conidia were ellipsoid to barrel-shaped, 23 to 39 × 12 to 19 µm, with a length/width ratio of 1.4 to 2.3 and devoid of fibrosin bodies. Germ tubes were produced in the perihilar position of the conidia. Primary conidia were apically rounded and basally subtruncated. No chasmothecia were found until the plants died in winter. The morphological characteristics were typical for anamorph of the genus Golovinomyces. To identify the fungus, genomic DNA was extracted from the four herbarium specimens (KUS-F 28650, 30839, 31728, and 31787). PCR products were amplified using the primer sets PM10/ITS4 for internal transcribed spacer (ITS) and PM3/TW14 for the large subunit (LSU) of the rDNA (Mori et al. 2000, Bradshaw and Tobin 2020). Sequences obtained in the present study were deposited at GenBank (accession numbers ON834488-91 for ITS and ON834494-7 for LSU). A BLASTn search of the Korean specimens showed 100% identity with reference sequences of G. ambrosiae in GenBank (KX98730, MK452580, and MK452588 for ITS and MF612182, MK452653, and MK452661 for LSU). In phylogenetic trees of a concatenated dataset of the ITS and LSU sequences, the Korean specimens formed a well-supported clade with the reference sequences of G. ambrosiae. Pathogenicity tests were carried out by touching and dusting an infected leaf (KUS-F 31787) onto the upper leaf surface of five healthy plants. Five non-inoculated plants served as controls. After two weeks, all inoculated plants formed white patches on the surface of leaves and stems, whereas the control plants remained symptomless. The fungus on the inoculated plants was identical to that observed on the initially diseased plant, fulfilling Koch's postulates. As a result, the causal agent of the powdery mildew on L. vulgare was confirmed as G. ambrosiae (Schwein.) U. Braun & R.T.A. Cook, based on the current taxonomy and nomenclature of this species by Qiu et al. (2020).. Previously powdery mildew collections on L. vulgare have been reported as Golovinomyces cichoracearum (≡ Erysiphe cichoracearum) s. lat. in Estonia, Finland, Germany, and Switzerland, Golovinomyces biocellatus in Spain, and Podosphaera fusca (probably P. xanthii according to the current taxonomy) in the former Soviet Union (now Russia and adjacent countries) (Farr and Rossman 2022). This study is the first report of powdery mildew disease caused by G. ambrosiae on L. vulgare in Korea. Qiu et al. (2020) confirmed the occurrence of G. ambrosiae on L. maximum, another species of the genus Leucanthemum. As powdery mildew causes damage to the cultivation of L. vulgare by loss of ornamental value, appropriate control measures should be developed.

Revisiting Rhytisma lonicericola: Morphological Characterization and Molecular Phylogenetic Analysis.

Rhytisma lonicericola was identified as a tar spot fungus on Lonicera sp. in 1902, and has since been recorded on several species of Lonicera in China, Japan, and Korea. Most of the previous records of R. lonicericola have been based on a list of disease occurrences in the absence of any formal morphological identification or molecular analyses. Using six newly obtained specimens collected in the past 2 years, we confirmed the tar spot fungus found on L. japonica in Korea as R. lonicericola based on morphological examinations and molecular phylogenetic analyses. This fungus was distinguished from R. xylostei, another tar spot fungus on Lonicera, by ascospore size and geographical distributions. We present detailed mycological information and, for the first time, DNA sequence data useful for the identification of R. lonicericola.

First Report of Leaf Spot Caused by Septoria erigerontis on Conyza sumatrensis in Korea.

Conyza sumatrensis (Retz.) E. Walker (syn. Erigeron sumatrensis) or commonly known as fleabane, is an annual herbaceous plant native to South America. It/span>was accidentally introduced to Korea in the 1930s and became invasive in natural and managed ecosystems of the country (Kim et al. 2008). Leaf spots on this plant were first observed in March 2013 in Jeju (33°29'45"N; 126°26'26"E), and then in February 2017 in Seoguipo (33°14'30"N; 126°32'58"E), Korea. The severity of the disease was estimated to be greater than 50%. Initial symptoms were small, distinct, reddish-brown, then turned into brown spots with dark purplish-brown margins. Conidiomata were pycnidial, epigenous, occasionally hypogenous, scattered, dark brown to rusty brown, globose, embedded in host tissue or partly erumpent, 70 to 165 µm in diameter, with ostioles measuring 10 to 26 µm in diameter. Conidia were straight to flexuous, 24 to 65 × 1.5 to 2.0 µm, hyaline, and 1 to 5 septate. Morphological circumscriptions were consistent with Septoria erigerontis Peck (Verkley et al. 2013). To obtain a monoconidial isolate, conidia were collected from lesions, placed in an Eppendorf tube containing sterile water and streaked onto the surface of 2% water agar (WA) plates supplemented with 100 mg/L of streptomycin sulfate, and after five days transferred onto potato dextrose agar (PDA). The two-week-old colonies incubated at 25°C on PDA had a slightly ruffled, but mostly colorless margin; colonies were 5 to 7 mm in diameter, slightly elevated in the center, surface black, covered with a diffuse to a dense mat of grey aerial mycelium. Voucher specimens were housed in the Korea University Herbarium (KUS-F27274 and F29725), and two cultures were deposited in the Korea Agricultural Culture Collection (Accession Nos: KACC47219 and KACC48297). Nucleotide sequences of the internal transcribed spacer (ITS), translation elongation factor 1-α (EF), actin (ACT), 28S rDNA (LSU), and RNA polymerase II second largest subunit (RPB2) genes obtained from KACC47219 were determined (Verkley et al. 2013) and deposited in GenBank (Accession Nos: OM909018, OM908934, OM974318, OM974319, OM974320). Results of BLASTn search for ITS and LSU were 99-100% identical with reference sequences of Septoria erigerontis (MH865036, MH876473), S. lactucae (MK617321), and S. phlogis (MH876550) in GenBank. Whereas it showed 97% similarity for ACT, 93-94% for EF and RPB2 genes with sequences of S. erigerontis (JQ325031, KF253363, KF252411). Pathogenicity was tested by spraying 20 leaves of four-month-old three potted plants with a conidial suspension (1×104 propagules/mL) harvested from a four-week-old culture (span style="font-family:'Times New Roman'">KACC47219). Ten leaves were used as controls. The plants were placed in a dew chamber at 26°C for 24 h, then moved to a greenhouse. Inoculated leaves developed typical symptoms after seven days, whilst no symptoms were observed on control ones. S. erigerontis was re-isolated from symptomatic lesion and its identity was confirmed by microscopic studies, fulfilling Koch's postulates. Although S. erigerontis has been recorded to be associated with leaf spots of Erigeron spp. and Conyza spp. (Farr and Rossman 2022), there is no previous record of this fungus on C. sumatrensis. To our knowledge, this is the first report of leaf spot caused by S. erigerontis on C. sumatrensis worldwide as well as in Korea. We presume that this fungus may have potential as a biocontrol agent on fleabanes, particularly glyphosate-resistant Conyza species (Sansom et al. 2013). References: Farr, D. F., and Rossman, A. Y. Fungal Databases, Syst. Mycol. Microbiol. Lab., Online publication. ARS, USDA. Accessed 6 February 2022. Kim, C. S., et al. 2008. Korean J. Weed Sci. 28:42. Sansom, M., et al. 2013. Plant Protect. Sci. 49:44. Verkley, G. J. M., et al. 2013. Stud. Mycol. 75:213.

First Report of Powdery Mildew Caused by Podosphaera xanthii on Cucurbita ficifolia in Korea.

Cucurbita ficifolia Bouché, called fig-leaf gourd, is a cucurbitaceous climbing plant native to the Americas. During summer and autumn of 2020, almost all of fig-leaf gourds planted in an experimental plot in Jeonju (35°50'54″N, 127°07'46″E), Korea, were found to be infected by a powdery mildew with a 100% disease severity. Symptoms first appeared as white, small, irregular colonies, later coalesced into abundant hyphal growth on both sides of the leaves and young stems. Subsequently premature senescence and poor growth of affected leaves was observed. A voucher specimen was housed in the Korea University herbarium (KUS-F32173). For morphological characterization of the fungus, fresh materials were used for microscopy. Conidiophores (n = 30) were straight, 90 to 190 × 10 to 12 µm and produced three to six immature conidia in chains with a crenate outline. Conidia (n = 30) were ellipsoid-ovoid to barrel-shaped, measured 28 to 38 × 18 to 24 µm with a length/width ratio of 1.3 to 2.0, and contained distinct fibrosin bodies. No chasmothecia were found over the course of the season. The morphological feature of the fungus and the host genus were compatible with those of Podosphaera xanthii (Castagne) U. Braun & Shishkoff (Braun and Cook 2012), a well-known cucurbitaceous powdery mildew. For further confirmation, DNA was extracted from mycelium taken from above mentioned specimen. Internal transcribed spacers (ITS1 and ITS2) and large subunit (LSU) gene of the rDNA were amplified using primer pairs ITS1F/PM6 and PM3/TW14, respectively (Takamatsu and Kano 2001). Newly obtained sequences were registered to the GenBank under the accession numbers OL677355 for ITS and OL677356 for LSU. Our sequences shared 99.54~99.77% identity for ITS (MW559231 and MT250855) and 99.58% for LSU with sequences of P. xanthii (MK357445 and MK357438) in BLAST'n search. Pathogenicity tests were performed twice by pressing method of mycelial patches of the infected leaf onto the young leaves of five healthy fig-leaf gourd plants. Five non-inoculated plants were used as controls. Inoculated leaves started to develop powdery mildew signs after 5 days treatment, whereas the control plants remained symptomless. The fungus on the inoculated plants was morphologically identical to that originally observed on diseased plants, fulfilling Koch's postulates. To date three powdery mildew species have been reported on C. ficifolia (Farr and Rossman 2021). Among these reports, Golovinomyces orontii sensu lato was known from Chile, Mexico, United Kingdom, and Germany, Leveillula taurica from Korea and Podosphaera fuliginea (currently P. xanthii) was recorded Australia and India. To our knowledge, this is the first report of P. xanthii on C. ficifolia in Korea. Since this plant is used as grafting rootstock for preventing soil-borne gummy stem blight of cucumber caused by Didymella bryoniae in Korea (Choi et al. 2009), economic importance of the powdery mildew occurring on leaves of this plant is currently limited. Nevertheless, presence of a powdery mildew could be informative to breeding program of Cucurbita spp. and safe production of C. ficifolia fruits globally.

First Report of Coleosporium clematidis Causing Rust Disease on Clematis patens in Korea.

Clematis patens (Ranunculaceae), often called big-flower clematis, is a perennial plant native to Northeast Asia, including China, Japan, and Korea. This plant is one of the popular ornamental plants because of its large and colorful flower. In Korea, it is widely cultivated for public and private gardening and medicinal purposes. In September of 2021, symptoms of rust disease were found on C. patens at a public park (ca. 30 ha) in Jeonju (35°52'16"N, 127°03'16"E), Korea, where the disease occurred on 80% of C. patens plants (n = 50) surveyed, and disease severity in each affected plant ranged 60 to 90%. Symptoms appeared as light green, vein-limited chlorotic spots on the upper surface of infected leaves, and yellow or orange rust pustules were formed on the corresponding lower surface of leaves. A representative sample was deposited in the Kunsan National University Herbarium (KSNUH1522). Uredinia were yellow or orange, round to ellipsoidal, mostly scattered, and 0.5-1 mm in diameter. Urediniospores were pale yellow, ellipsoid or ovoid, 23.1 to 34.8 × 14.9 to 24.7 (average 29.3 ± 2.7 × 18.8 ± 2.2 µm [mean ± SD], n = 50) µm with a verrucose and hyaline wall of 1.0-2.0 µm thick. The morphological characteristics were similar to those reported for Coleosporium clematidis (Barclay 1889, Hiratsuka et al. 1992). To confirm morphological identification, genomic DNA was extracted from a representative specimen (KSNUH1522). The internal transcribed spacer (ITS) rDNA with primers ITS5-u and ITS4rust (Pfunder and Schürch 2001) and large subunit (LSU) rDNA with primers LRust1R and LRust3 (Beenken et al. 2012) were amplified for sequencing. Two resulting sequences (Acc. Nos. OM200310 for ITS, OM184262 for LSU) were blasted in GenBank. The ITS sequence of the Korean sample differs at a nucleotide with a sequence of C. clematidis from Clematis sp. (KX386005) but at eight nucleotides with other three sequences of C. clematidis (KX386007, KX386008 and KX386010). The LSU sequence differs at a nucleotide from the sequences of C. clematidis from Clematis sp. (KX386039, KX386040, KX386042). In phylogenetic trees of the ITS and LSU sequences, the Korean isolate formed a well-supported clade with the reference sequences of C. clematidis. For a pathogenicity test, urediniospores (1.25 ×106/ml) were harvested from the infected leaves and inoculated onto three healthy C. patens. Three non-inoculated plants served as controls. Inoculated and non-inoculated plants were kept in a plant growth chamber at 22°C, a 16/8 h of light cycle, 80% humidity. After three weeks, all inoculated plants formed yellow rust pustules on the lower surface of leaves, identical to what was previously observed in the field, whereas the control plants remained symptomless. The same pathogen was confirmed from the symptomatic plants, fulfilling Koch's postulates. Based on morphological characteristics, sequence data and pathogenicity test, the causal agent of rust on Clematis patens was identified as C. clematidis. To our knowledge, this is the first report of rust disease caused by C. clematidis on C. patens in Korea and previously recorded only in Japan (Hiratsuka et al. 1992). Coleosporium clematidis has been reported on about 60 species of Clematis in Asia and Africa but has not been reported in Europe and North America (Farr and Rossman 2022). In Korea, Clematis fusca var. violacea was previously reported as a host plant for the causal pathogen (Cho and Shin 2004). Given the high occurrence and severe damage, this disease could be a potential threat to the cultivation of C. patens.

Emergence of a New Rust Disease of Virginia Creeper (Parthenocissus quinquefolia) through a Host Range Expansion of Neophysopella vitis.

Virginia creeper (or five-leaved ivy; Parthenocissus quinquefolia) is one of the most popular and widely grown climbers worldwide. In September 2021, Virginia creeper leaves with typical rust symptom were found in an arboretum in Korea, with severe damage. Globally, there is no record of a rust disease on Virginia creeper. Using morphological investigation and molecular phylogenetic inferences, the rust agent was identified as Neophysopella vitis, which is a rust pathogen of other Parthenocissus spp. including Boston ivy (P. tricuspidata). Given that the two ivy plants, Virginia creeper and Boston ivy, have common habitats, especially on buildings and walls, throughout Korea, and that N. vitis is a ubiquitous rust species affecting Boston ivy in Korea, it is speculated that the host range of N. vitis may recently have expanded from Boston ivy to Virginia creeper. The present study reports a globally new rust disease on Virginia creeper, which could be a major threat to the ornamental creeper.

Kordyana commelinae Associated with White Smut-like Disease on Commelina communis and C. minor in Korea.

A fungus of the genus Kordyana, found on leaves of Commelina communis and C. minor exhibiting white smut-like symptoms, was identified as Kordyana commelinae based on morphological characteristics and two rDNA sequence analyses. We report the novel occurrence of the genus Kordyana in Korea and the association of K. commelinae with the host plant species. As well, we provide the necessary mycological information to resolve species delimitation and taxonomic problems of Kordyana.

First Report of Powdery Mildew Caused by Golovinomyces ambrosiae on Verbena bonariensis in Korea.

Verbena bonariensis L., named as purple-top vervain or Argentinian vervain, is native to tropical South America. It is cultivated worldwide as an ornamental plant. During summer and autumn of 2020, over 50% of the leaves of V. bonariensis were found infected with powdery mildew in a flower garden in Seoul (37°35'19"N 127°01'07"E), Korea. White, superficial mycelia developed initially on the leaves and subsequently covered surfaces of leaves and stems, are resulting in leaf discoloration, early defoliation, and shoots distortion. Heavily infected plants lost ornamental value. A representative voucher specimen was deposited in the Korea University herbarium (KUS-F32168). Morphological characterization and measurements of conidiophores and conidia were carried out using fresh samples. Microscopic observation showed that aAppressoria on the superficial hypha were nipple-shaped, but rarely found or nearly absent. Conidiophores (n = 30) were cylindrical, 110 to 220 × 10 to 12 µm, and produced 2 to 5 immature conidia in chains with a sinuate outline, followed by 2 to 3 short cells. Foot-cells of conidiophores were straight, cylindrical, and 46 to 90 µm long. Conidia (n = 30) were hyaline, ellipsoid to doliiform, 28 to 40 × 18 to 24 µm with a length/width ratio of 1.3 to 2.0, and contained small be like oil-like drops, but without distinct fibrosin bodies. Primary conidia were apically rounded and sub-truncate at the base. Germ tubes were produced at perihilar position of the conidia. Chasmothecia were not observed. These morphological characteristics were typical of the conidial stage of the genus Golovinomyces (Braun and Cook 2012, Qiu et al. 2020). To identify the fungus, rDNA was extracted from the voucher sample. PCR products were amplified using the primer pair ITS1F/PM6 for internal transcribed spacer (ITS), and PM3/TW14 for the large subunit (LSU) of the rDNA (Takamatsu and Kano 2001). The resulting sequences were registered to GenBank (MW599742 for ITS, and MW599743 for LSU). Using Blast'n search of GenBank, sequences showed 100% identity for ITS and LSU with G. ambrosiae (MT355557, KX987303, MH078047 for ITS, and AB769427, AB769426 for LSU), respectively. Thus, based on morphology and molecular analysis, the isolate on V. bonariensis in Korea was identified as G. ambrosiae (Schwein.) U. Braun & R.T.A. Cook. Pathogenicity tests were carried out by touching an infected leaf onto healthy leaves of disease-free pot-grown plants using a replication of five plants, with five non-inoculated plants used as controls. After 7 days, typical powdery mildew colonies started to appear on the inoculated leaves. The fungus on inoculated leaves was morphologically identical to that originally observed in the field. All non-inoculated control leaves remained symptomless. On different global Verbena species, tThere have been many reports of Golovinomyces powdery mildews including G. cichoracearum s.lat., G. longipes, G. monardae, G. orontii s.lat., and G. verbenae (Farr and Rossman 2021). In China, G. verbenae was recorded on V.erbena phlogiflora (Liu et al. 2006). Golovinomyces powdery mildew has not been reported on Verbena spp. in Korea. Powdery mildew has been reported on V. bonariensis in California, but identity of the causal agent had not been reported. To our knowledge, this is the first report on the identity of the powdery mildew caused by G. ambrosiae on V. bonariensis in Korea. Since heavily infected plants lost ornamental value, appropriate control measures should be developed.

First Report of Powdery Mildew Caused by Podosphaera xanthii on Benincasa hispida in Korea.

Benincasa hispida (Thunb.) Cogn. (syn. B. cerifera Savi, Cucurbita hispida Thunb.), called wax gourd or ash gourd, is a cucurbitaceous vine grown for medicinal purposes and commercial values of its large fruits in Southeast Asia (Al-Snafi 2013). During the summer and autumn of 2020, leaves of wax gourd were observed to be affected by powdery mildew with 100% disease incidence in an experimental plot of Jeonbuk National University (35°50'55″N, 127°07'48″E), Korea. Fungal colonies were initially circular to irregular, forming white patches on both sides of the leaves and young stems, finally covering entire leaves and causing premature senescence of the leaves and poor growth. A representative voucher specimen was deposited in the Korea University herbarium (KUS-F32171). At least 30 measurements were taken for each asexual diagnostic features. Conidiophores arising from superficial hyphae were straight, 100 to 210 µm long, and produced 3 to 7 immature conidia in chains with a crenate outline. Foot-cells were cylindrical, 46 to 74 ×10 to 12 µm, followed by 1 to 2 shorter cells. Conidia were ellipsoid-ovoid to barrel-shaped, 30 to 40 × 18 to 23 µm with a length/width ratio of 1.4 to 2.0 and contained conspicuous fibrosin bodies. Germ tubes were produced from a lateral position on conidia. Sexual stage was not observed during the growing season. The morphological characteristics of the fungus were compatible with those of Podosphaera xanthii (Castagne) U. Braun & Shishkoff (Braun and Cook 2012), a well-known cucurbitaceous powdery mildew. DNA was extracted from mycelium, and primer sets ITS1F/PM6 and PM3/TW14 were used for amplification of ITS1-5.8S-ITS2 regions and 5´-end of 28S rDNA gene, respectively (Takamatsu and Kano 2001). Sequences determined in this study were deposited to the GenBank under the accession numbers MW559231 and MW559420, respectively. The sequences for ITS regions and 28S rDNA gene showed 99.78% and 99.07% similarity respectively with those of P. xanthii (MH465242, MH465243, MT250855 for ITS, and MK357436, MT826247 for LSU). Pathogenicity was confirmed twice by pressing a diseased leaf onto young leaves of five wax gourd plants. Five non-inoculated plants were used as controls. Inoculated leaves developed symptoms after 5 days, whereas the control plants remained symptomless. The fungus present on the inoculated plants was identical morphologically to that originally observed on diseased plants. Sphaerotheca fuliginea (syn. P. xanthii) on B. hispida has been listed in Hungary, India, Japan, Singapore, and Taiwan so far (Farr and Rossman 2021). Recently, the identity of P. xanthii on B. hispida in Taiwan was confirmed with morphological examination and molecular analysis by Wu and Kirschner (2017). To our knowledge, this is the first report of powdery mildew caused by P. xanthii on B. hispida in Korea. Since wax gourd production is only recently started on a commercial scale in the southern part of Korea, powdery mildew infections pose a serious threat to the safe production of the fruits, especially in organic farming where chemical control options are limited.