Ji-Hyun Park

Marsh mallow (Althaea officinalis L., Malvaceae) is used both as a medicinal and an ornamental plant (Shah et al. 2011). In August 2014, Choanephora blight was observed on flowers of A. officinalis in an experimental plot of Jeollabuk-do Agricultural Research and Extension Services (35°56'38.44"N; 126°59'37.14"E) in Iksan, Korea. Initially water-soaked lesions appeared on the petals and monosporous sporangiola developed along the edge of the petal, causing discoloration of the flowers. Eventually the flowers were rapidly withered and rotted, leading to flower blight. However, no symptoms were found on the stems and leaves. Approximately 20% of the flowers on plants were affected in the beds. A representative specimen was deposited in the Korea University Herbarium (KUS-F29113). A fungal isolate was established by placing monosporous sporangiola, obtained from infected tissue, on potato dextrose agars (PDA). Fungal colonies covering the plate (diam. 90 mm) in 48 hours were white at first with abundant aerial mycelia, and subsequently turned pale yellow with abundant sporangiola. Sporangiola were indehiscent, ellipsoid to broadly fusiform, brown to dark brown, longitudinally striate, and 8 to 12 μm wide and 12 to 25 μm high. Sporangia with a few or many sporangiospores were subglobose to globose, pale brown to brown, and 55 to 145 μm in diameter. Sporangiospores from sporangia were broadly ellipsoid to ovoid, brown to pale brown, striate, 8 to 12 μm wide and 16 to 22 μm high, with hyaline appendages at both ends. Zygospores were not observed. Based on these characteristics, the fungus was identified as Choanephora cucurbitarum (Berk. & Ravenel) Thaxt. (Kirk 1984). To confirm the identification, genomic DNA was extracted with the DNeasy Plant Mini Kit (Qiagen Inc., Valencia, CA). The primers ITS1/ITS4 and NL1/LR3 were used for amplifying and sequencing the internal transcribed spacer (ITS) region and the D1/D2 region of the large subunit (LSU) of nuclear ribosomal DNA, respectively (Walther et al. 2013). GenBank BLAST analysis of the D1/D2 sequence showed that the sequence (KU316935) belonged to the genus Choanephora, whereas the ITS sequence (KU316934) identified the species as C. infundibulifera f. cucurbitarum (syn. C. cucurbitarum) based on 100% identity to accessions KM200034 (ex Hosta plantaginea) and KP406599 (ex Phlox paniculata) and >99% similarity to accession JN206234. A pathogenicity test was performed by spraying 3 cut-flowers in a vase of water with a sporangiola suspension (2 × 10⁴ cells/ml). Another 3 cut-flowers in the same conditions were treated with sterilized water as controls. The flowers were covered with plastic bags for 24 h and then transferred to a greenhouse (28°C and 60-80% RH). On 2 to 3 days post-inoculation, water-soaked lesions appeared on the petals of inoculated flowers. No symptoms were observed on controls. C. cucurbitarum was re-isolated from inoculated flowers, fulfilling Koch’s postulates. Choanephora infundibulifera as well as C. cucurbitarum have been reported on many malvaceous plants, but not on Althaea species (Farr and Rossman 2015). This is the first report of C. cucurbitarum on A. officinalis globally as well as in Korea.

Tragopogon dubius Scop., known as western salsify, is native to southern and central Europe and western Asia, but currently is a notorious invasive plant in many countries, including North America. This plant has widely been naturalized and disturbing native plant communities in Korea after being introduced accidentally in the early 1990s (Park 1999). In July 2015, dozens of plants exhibiting powdery mildew symptoms were found in Daegu (35°50'21.4"N 128°27'56.6"E), Korea. Powdery mildew colonies first appeared as thin, white patches, but soon progressed to abundant hyphal growth on both sides of the leaves and stems. Severe infections caused leaf withering and premature senescence. Three voucher specimens were deposited in the Korea University Herbarium (KUS-F28770, F28790, F28801). Appressoria on the mycelium were lobed. Conidiophores measured 90 to 170 × 10 to 12 μm, were arising laterally from hyphal mother cells, and produced 2 to 5 immature conidia in chains with a sinuate outline, followed by 2 to 3...

Oilseed rape, Brassica napus L. (Brassicaceae), is grown worldwide for the production of vegetable oil for human consumption, animal feed, and biodiesel. In October 2015, powdery mildew was found on oilseed rape plants growing in a shaded area of a garden in Gapyeong (37°46'09.6"N 127°27'23.7"E), Korea. Symptoms began as thin, white colonies and later progressed to abundant growth on the leaves and stems, resulting in premature senescence. A representative sample was deposited in the Korea University Herbarium (KUS-F28881). Appressoria on the mycelium were well-developed, lobed, and solitary or in pairs. Conidiophores were cylindrical, 65 to 100 × 8 to 10 µm, and composed of 3 to 4 cells. Foot-cells of conidiophores were straight, cylindrical, 16 to 38 µm long and generally equal to or shorter than the upper cells. Singly produced conidia were oblong to cylindrical or oval, 32 to 47 × 13 to 19 µm (length/width ratio = 2.0 to 2.7), and lacked distinct fibrosin bodies. Germ tubes developed on the perihilar ...

Japanese honeysuckle (Lonicera japonica Thunb., Caprifoliaceae) is native to China, Japan and Korea, and has become naturalized and is now invasive in Australia, New Zealand, Argentina, Brazil, Mexico, and much of the United States (Schierenbeck 2004). In Korea, it is widely planted as an effective groundcover and also as a fragrant ornamental. In October 2000, several vines exhibiting signs and symptoms of powdery mildew were found in Seoul, Korea. White superficial mycelia and conidia were present on both sides of the leaves as well as on young shoots, forming thin, irregular colonies. Infections often caused red-purplish discolorations and leaf senescence. Similar symptoms have also been found in Pyeongchang, Samcheok, Suwon, Gapyeong, and Busan from 2000 to 2015. Fourteen voucher specimens were deposited in the Korea University Herbarium (KUS). Conidiophores were unbranched, cylindrical, 50 to 130 µm and composed of 3 to 4 cells. Foot-cells in conidiophores were slightly to moderately flexuous. Conidia produced singly, were ellipsoid or doliiform, 27 to 40 × 15 to 21 µm, and devoid of distinct fibrosin bodies. Germ tubes were formed on the perihilar position of the conidium. The surface of the conidia had an angular/rectangular wrinkling pattern. Chasmothecia were dark brown, spherical, and scattered subgregariously, 100 to 140 µm in diameter. Each chasmothecium contained 4 to 6 asci. Appendages were 3 to 5 times dichotomously branched, aseptate or 1- septate, 11 to 17 per chasmothecium, 1.0 to 1.7 times as long as the chasmothecial diam. and brown at the base, becoming paler towards the tip. Asci were short stalked, 4 to 6 spored, and 55 to 67 × 37 to 47 µm. Ascospores were ellipsoid-ovoid, and 15 to 20 × 8 to 12 µm. The features were compatible with those of Erysiphe lonicerae var. lonicerae DC. (Braun and Cook 2012). The internal transcribed spacer regions of rDNA from KUS-F27344 and F28645 were amplified using primers ITS1/ITS4, and sequenced (Takamatsu et al. 2009). Phylogenetic analysis (MEGA 6) using the neighbor-joining method showed that two Korean isolates (GenBank Accession Nos. KT748729 and KT748730) grouped with E. lonicerae var. lonicerae on Lonicera spp. (GenBank Accession Nos. LC010020, LC009991, LC009963). Pathogenicity was confirmed by gently pressing an infected leaf onto ten leaves of a healthy, potted vine. Ten non-inoculated leaves of similar features served as controls. All inoculated leaves developed symptoms after 8 to 10 days, whereas the control leaves remained symptomless. The powdery mildew infections associated with E. lonicerae var. lonicerae on Japanese honeysuckle have been recorded in Japan, China, and Switzerland (Farr and Rossman 2015). To our knowledge, this is the first report of powdery mildew caused by E. lonicerae var. lonicerae on Japanese honeysuckle in Korea. Our field observations suggest that the disease would be a serious threat to the widespread ornamental plantings of Japanese honeysuckle in Korea, especially in the case where the vines are growing in the shade.

Juglans mandshurica Maxim., known as Manchurian walnut, is a deciduous tree native to China, Russian Far East, and Korea. It is an ecologically important tree of forest community in Korea. In October 1999, several trees shown symptoms of powdery mildew were found in Anyang, Korea. Initial symptoms were small, circular, powdery, white colonies on abaxial leaf surface. Later, light yellow spots formed on the adaxial leaf surface corresponding to the powdery mildew colonies of abaxial leaf surface. Each colonies enlarged and coalesced to cover the whole abaxial surface, followed by early senescence and premature defoliation. Powdery mildew lesions with abundant chasmothecia were found in October. The similar symptoms have also been found in Hongcheon and Suwon from 1999 to 2014. Seven voucher specimens were deposited in the Korea University Herbarium (KUS). Hyphal appressoria were hook-shaped, often branched, and single or opposite in pairs. Conidiophores were erect, cylindrical, 160 to 280 × 6 to 8 μm, stra...