Dong-Wan Kang

Pink Mold Rot on Unishiu Orange (Citrus unshiu Mac.) Caused by Trichothecium roseum (Pers.) Link ex Gray in Korea

In 2012, a pink mold rot was observed on unishiu orange (Citrus unshiu Mac.) fruits at the Wholesale Market for Agricultural Products, Jinju, Korea. The symptom on unishiu orange was a water-soaked lesion on the surface of fruit, which later on enlarged to form softened brown rot lesions. The diseased fruits were covered with pink-colored mold, consisting of conidia and conidiophores of the pathogen. Optimum temperature for mycelial growth was . Conidia were hyaline, smooth, 2-celled, and thick-walled conidia with truncate bases, ellipsoidal to pyriform, characteristically held together zig-zag chains and in size. Conidiophore was erect, colorless, unbranched, and 4-5 wide. On the basis of mycological characteristics, pathogenicity test, and molecular analysis with complete ITS rDNA region, the causal fungus was identified as Trichothecium roseum (Pers.) Link ex Gray. This is the first report of pink mold rot caused by T. roseum on unishiu orange in Korea.

Stem Rot of Convallaria keiskei Caused by Sclerotium rolfsii

Stem rot symptoms of Convallaria keiskei occurred sporadically in the herb exhibition field at Hamyang-gun Gyeongnam province in Korea. The typical symptom is water-soaking on the main stem, rotting, wilting, and blighting, which eventually leads to death of the plant. The sclerotia, which were white to brown in color, globoid in shape with size of 1~3 mm hyphal width of which was 4~9 μm, were formed over lesions and surface soil line. The optimum temperature for mycelial growth and sclerotia formation was 30 o C on PDA. The typical clamp connections were observed in the hyphae of the fungus grown on PDA. Mycological characteristics and pathogenicity to host plants indicated that the infected fungus was Sclerotium rolfsii Saccardo. This is the first report of stem rot on Convallaria keiskei caused by S. rolfsii in Korea.

Identification of Lasiodiplodia pseudotheobromae causing mango dieback in Korea

Abstract Mango (Mangifera indica) is an economically important fruit grown in tropical regions. Mango cultivation has increased in Korea as the fruit has become more popular; however, the majority of the fruit is imported. Mango dieback was observed for the first time in July 2016, in Tongyeong, South Korea. The aim of the present study was to identify the causal pathogen. Identification of the fungus was based on morphological and cultural characteristics, and sequencing of the internal transcribed spacer rRNA region and gene encoding translation elongation factor 1-alpha. A phylogenetic analysis of the sequences confirmed that the fungus isolated from diseased mango plants was Lasiodiplodia pseudotheobromae. Koch’s postulates were completed by pathogenicity tests conducted on healthy leaves, fruit and whole plants. Based on the morphological characteristics, pathogenicity tests, and molecular identification, the causal fungus was identified as L. pseudotheobromae. This is the first report of mango dieback caused by L. pseudotheobromae in Korea. The recent occurrence of the disease indicates that the fungus poses a potential threat to mango production in Korea.

Occurrence of Sclerotium Rot of Corn Caused by Sclerotium rolfsii in Korea

The sclerotium rot of corn (Zea mays L.) occurred sporadically at the experimental field of Gyeongsangnam-do Agricultural Research and Extension Services in July 2011. The infected stems were water-soaked, wilted, and finally led to the death of the whole plants. White mycelial mats were spread over lesions, and then sclerotia were formed on stem and near soil line. The sclerotia were globoid in shape, white to brown in color and 1-3 mm in size. The hyphal width was . The optimum temperature for mycelial growth and sclerotia formation on PDA was 30 on PDA. The typical clamp connections were observed in the hyphae of the fungus grown on PDA. On the basis of mycological characteristics and pathogenicity to host plants, this fungus was identified as Sclerotium rolfsii Saccardo. This is the first report of sclerotium rot on corn caused by S. rolfsii in Korea.

Occurrence of Sclerotium Rot in Allium tuberosum Caused by Sclerotium rolfsii in Korea

Abstract In this study, we characterized sporadically occurring sclerotium rot caused by Sclerotium rolfsii in Chinese chive (Allium tuberosum Roth.) in farm fields in Sacheon, Korea. The initial symptom of the disease was water-soaked, which progressed to rotting, wilting, blighting, and eventually death. Further, mycelial mats spread over the lesions near the soil line, and sclerotia formed on the scaly stem and leaves. The sclerotia were globoid, 1~3 mm, and white to brown. The optimum temperature for growth and sclerotia formation on potato dextrose agar (PDA) was 30°C. The diameter of the hypae ranged from 4 to 8 μm. Clamp connection was observed on PDA medium after 5 days of incubation. Based on the mycological characteristics, internal transcribed spacer sequence analysis, and pathogenicity test, the causal agent was identified as Sclerotium rolfsii Saccardo. This is the first report of sclerotium rot in Chinese chive caused by S. rolfsii in Korea.

The occurrence of leaf blight on Ophiopogon japonicus caused by Phyllosticta ophiopogonis in Korea

A severe outbreak of Phyllosticta leaf blight was observed on mondo grass (Ophiopogon japonicas) in Jinju, South Korea during 2013–2014. Symptoms initially appeared on chlorotic leaves, followed by blight and finally leaf death. DNA sequencing and phylogenetic analysis of the internal transcribed spacer rRNA gene region confirmed that the isolate was Phyllosticta ophiopogonis. Koch’s postulates were supported by pathogenicity tests conducted on healthy plants. Based on morphological characteristics, pathogenicity tests, and molecular analysis, the causal fungus was identified as P. ophiopogonis. To the best of our knowledge, this is the first report of leaf blight caused by P. ophiopogonis on mondo grass in South Korea.

Soft Rot on Peach Caused by Rhizopus oryzae in Korea

In July and August 2011, a disease suspected to be Rhizopus soft rot was observed on peach (Prunus persica var. vulgaris) at the Wholesale Market for Agricultural Products, Jinju, Korea. The first symptom of soft rot on peach is a water-soaked appearance of the affected tissue. The infected parts later disintegrated into a mushy mass of disorganized cells followed by rapid softening of the diseased tissue. The lesion on peach was rapidly softened and rotted, then became brown or dark brown. Optimum temperature for mycelial growth of the causal fungus on PDA was and growth was still apparent at Sporangiophores were 6~20 in diameter. Sporangia were globose and 35~200 in size. The color of sporangia was brownish-grey to blackish-grey at maturity. Sporangiospores were sub-globose, brownish- black streaked and 5~10 in size. Columella were globose to sub-globose and 85~120 in size. On the basis of mycological characteristics, pathogenicity test, and molecular identification, the causal fungus was identified as Rhizopus oryzae Went & Prinsen Geerligs. To our knowledge, this is the first report of soft rot caused by R. oryzae on peach in Korea.

Stem Rot of Common Bean (Phaseolus vulgaris L.) Caused by Sclerotium rolfsii

Crop Environment Research Division, National Institute of Crop Science, RDA, Suwon 441-857, Korea(Received on May 29, 2012; Revised on June 7, 2012; Accepted on June 8, 2012)Stem rot symptoms of common bean occurred sporadically in Jinju, Korea. The typical symptom includedwater-soaking on the main stem, rotting, wilting, and blighting, which eventually leads to death of the plant.The sclerotia, white to brown, spherical with size of 1

Stem Rot of Stachys sieboldii Caused by Sclerotium rolfsii in Korea

Stem rot of Stachys sieboldii occurred sporadically in the farmer`s fields at Shindeung-myeon, Sancheonggun, Gyeongnam province in Korea. The infected leaves and stems are water-soaked, rotted, wilted and finally leads to the death of the whole plants. The sclerotia, 1-3 mm, white to brown, globoid, were formed on lesions and the surface of soil line. The optimum temperature for mycelial growth and sclerotia formation was on potato dextrose agar. The typical clamp connections were observed in the hyphae of the fungus. On the basis of mycological characteristics and pathogenicity to host plants, this fungus was identified as Sclerotium rolfsii Saccardo. This is the first report of stem rot on S. sieboldii caused by S. rolfsii in Korea.

Anti-quorum sensing and anti-biofilm formation activities of plant extracts from South Korea

Objective: To investigate anti-quorum sensing (anti-QS) and anti-biofilm formation (anti- BF) activities of the ethanol extracts of 388 plants. Methods: The anti-QS activity of the plant extracts was evaluated by disc-diffusion assays using the bio-reporter strain, Chromobacterium violaceum CV017. Pseudomonas aeruginosa PAO1, Yersinia enterocolitica ATCC 9610, and Agrobacterium tumefaciens C58, which possess QS systems, were used to evaluate the anti- BF activity of the plant extracts. Results: Among 388 plant extracts, the Cornus controversa (C. controversa) and Cynanchum wilfordii extracts exhibited the strongest anti-QS activity. The C. controversa extract exhibited anti-BF activity against Pseudomonas aeruginosa, Yersinia enterocolitica and Agrobacterium tumefaciens, whereas the Cynanchum wilfordii extract exhibited no anti-BF activity against Pseudomonas aeruginosa. In addition, the C. controversa extract suppressed soft rot of cabbage. Conclusions: The C. controversa extract inhibits bacterial QS and BF, and is capable of controlling soft rot. Therefore, this extract has potential for the prevention and treatment of bacterial infections and for the development of alternatives to antibiotics.