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 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 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.