Sang-Tae Seo

Diversity of Fungal Endophytes from Pinus koraiensis Leaves in Korea

The composition of endophytic fungal species from Pinus koraiensis was studied in two areas (Yeongwol and Jincheon), Korea. To identify 113 isolates, rDNA ITS regions were sequenced. On the basis of the ITS sequence, Pestalotiopsis sp. was the most frequently isolated species in both areas. Pestalotiopsis sp. (68.5%) and Lambertella sp. (12.4%) were isolated frequently in Yeongwol, whereas Pestalotiopsis sp. (41.7%), Hypoxylon sp. (20.8%) and Phomopsis sp. (12.4%) were dominant in Jincheon. Hypoxylon sp. and Phomopsis sp. were not found in Yeongwol.

Control Efficacy of Fungicides on Cherry Witches` Broom Caused by Taphrina wiesneri

In April 2008, cherry (Prunus yedoensis Matsumura) in Jeju exhibited severe disease of branches forming numerous twigs. Five isolates from diseased leaves were identified as Taphrina wiesneri on the basis of biological and genetic characteristics. Twenty one commercial fungicides were tested for control of the disease in vitro. Of the 21 fungicides, triazole compounds (difenoconazole, propiconazole and tebuconazole) showed relatively good antimicrobial activities. Results from the planta bioassays indicated that triazole compounds reduced the witches` broom disease showing control value compared with the nontreated controls.

First Report of Leaf Spot Caused by Corynespora cassiicola on Rose of Sharon in Korea

Rose of Sharon, Hibiscus syriacus L., is a flowering shrub in the family Malvaceae planted as the national flower of South Korea. In September 2012, previously unknown leaf spots with premature defoliation were observed on dozens of Rose of Sharon plants growing in the shaded area in a park of Dongducheon, Korea. The same symptoms were found on Rose of Sharon in several localities of Korea in 2012. The symptoms usually started as small, dark brown to grayish leaf spots, eventually causing leaf yellowing with significant premature defoliation. The diseased leaves retained for a while green color at the margin of the spots. Representative samples (n = 5) were deposited in the Korea University Herbarium (KUS). Conidiophores of the fungus observed microscopically on the leaf spots were erect, brown to dark brown, single or in clusters, amphigenous but mostly hypophyllous, and measured 80 to 400 × 5 to 10 μm. Conidia were borne singly or in short chains, ranging from cylindrical to broadest at the base and tapering apically, straight to slightly curved, pale olivaceous brown, 2 to 16 pseudoseptate, 50 to 260 × 9 to 20 μm, each with a conspicuous thickened hilum. On potato dextrose agar, single-spore cultures of two isolates were identified as Corynespora cassiicola (Berk. & M.A. Curtis) C.T. Wei on the basis of morphological and cultural characteristics (1,2). Two monoconidial isolates were preserved at the Korean Agricultural Culture Collection (KACC46956 and KACC46957). Genomic DNA was extracted using the DNeasy Plant Mini DNA Extraction Kit (Qiagen Inc., Valencia, CA). The complete internal transcribed spacer (ITS) region of rDNA was amplified with the primers ITS1/ITS4 and sequenced. The resulting sequences of 520 bp were deposited in GenBank (Accession Nos. KC193256, KC193257). A BLAST search in GenBank revealed that the sequences showed 100% identity with those of numerous C. cassiicola isolates from diverse substrates. To conduct a pathogenicity test, a conidial suspension (ca. 2 × 104 conidia/ml) was prepared in sterile water by harvesting conidia from 2-week-old cultures of KACC46956, and the suspension was sprayed onto the leaves of three healthy 2-year-old plants. Inoculated plants were kept in humid chambers for the first 48 h and thereafter placed in the glasshouse. After 10 days, typical leaf spot symptoms developed on the leaves of all three inoculated plants. C. cassiicola was reisolated from the lesions, confirming Kochs postulates. Control plants treated with sterile water remained symptomless. C. cassiicola is cosmopolitan with a very wide host range (1,2). Though Corynespora hibisci Goto was recorded to be associated with brown spot disease of H. syriacus in Japan (4), there is no previous record of C. cassiicola on H. syriacus (3). To our knowledge, this is the first report of Corynespora leaf spot on Rose of Sharon in Korea. According to our field observations in Korea, this disease was found in August and September, following a prolonged period of moist weather. Severe infection resulted in leaf yellowing and premature defoliation, reducing tree vigor and detracting the beauty of green leaves. References: (1) L. J. Dixon et al. Phytopathology 99:1015, 2009. (2) M. B. Ellis. Dematiaceous Hyphomycetes. Commonw. Mycol. Inst., Kew, UK, 1971. (3) D. F. Farr and A. Y. Rossman. Fungal Databases. Syst. Mycol. Microbiol. Lab., Online publication, ARS, USDA, Retrieved November 22, 2012. (4) K. Goto. Ann. Phytopathol. Soc. Japan 12:14, 1942.

Genotypic Characterization of Oak Wilt Pathogen Raffaelea quercus-mongolicae and R. quercivora Strains

Dept. of Forest Environment Protection, Kangwon National University, Chunchon 200-701, Korea(Received on September 3, 2010; Accepted on October 14, 2010)Recently, the oak wilt diseases especially on Quercus mongolica, have been increasing in various districts ofKorea. A collection of 38 strains of the oak wilt pathogen Raffaelea qeurcus-mongolicae and R. quecivoraisolated from Quercus spp. in Korea and Japan was characterized by β-tubulin gene sequence and randomlyamplified polymorphic DNA (RAPD) analysis. In cluster analysis based on β-tubulin gene sequence thestrains were divided into 4 clusters, of which clusters 2 and 4 were composed of Japanese strains except forone Korean strain. RAPD analysis showed that they were also effectively differentiated by a strong RAPDfragments. On the basis of the two genetic analysis, significant differences were detected between Koreanstrains and Japanese strains.Keywords : Raffaelea qeurcus-mongolicae, R. quecivora , RAPD, β-tubulin 국내에 분포하고 있는 참나무과(Fagaceae)에는 상수리나무, 갈참나무, 떡갈나무 및 신갈나무 등 약 23여종이보고되어 있으며(이, 1980), 이들 참나무과의 목재는 건축재, 가구재, 표고버섯 재배용 등으로 쓰이고, 껍질과 종자는 한약재, 코르크용 마개 등으로 쓰이는 유용한 나무이다. 이런 참나무과에 발생하는 병해로는 줄기썩음병,녹병, 뒷면흰가루병 및 잎오갈병 등이 보고되어 있다(한국식물병리학회, 2009). 참나무류 시들음병은 2004년 성남 이배재 지역에서 최초 발견되었으며, 국내 전국의 참나무과 나무, 특히 신갈나무를 중심으로 고사현상이 나타난 고사목으로부터 균을 분리하여 원인균을 Raffaeleaquercus-mongolicae로 동정하여 신종 보고하였으며, 이 병원균을 매개하는 매개충은 광릉긴나무좀(Platypus koryoensis)으로 밝혀졌다(Kim 등, 2009). 일본의 경우 1980년대부터 참나무과 나무의 쇠퇴 및고사 현상이 급속히 확산 발생되었다(Kuroda, 2001). 국내에 발생하는 참나무류 시들음병과 일본에서 발생하는참나무류 시들음병은 병원균, 피해 수종 및 병원균을 매개하는 매개충 등에서 차이를 보이고 있는데, 일본에 발생하는 참나무류 시들음병의 병원균은 R. quercivora로주 피해 수종은 물참나무와 졸참나무이며 매개충은 P.quercivorus로 보고되었다(Kubono와 Ito, 2002; Kuroda,2001). 그러나, 이들 병원균주들에 대한 유전적 관계를연구한 자료는 거의 없으며, Kim 등(2009)이 국내균의종동정을 위해 국내균과 일본균의 제한된 균주를 이용해18S rDNA, ITS rDNA, β-tubulin 유전자를 이용한 연구가 보고되어 있을 뿐이다. 본 연구에서는 국내 참나무류 시들음병균과 일본 참나

First report of brown spot needle blight on Pinus thunbergii caused by Lecanosticta acicola in Korea.

Pinus thunbergii Parl., known as black pine, is a pine native to coastal areas of Japan and Korea. Because of its resistance to pollution and salt, it is planted as windbreakers along the coast. In March 2010, needle blight symptoms were found on several trees of black pine in Naju, southern Korea. Further surveys in 2010 and 2011 showed that these symptoms are rather common but disease incidence is less than 1%. Small, circular grayish green spots first appeared on the needles. The spots developed into brown bands reaching 1 to 2 mm long, sometimes with yellow margins. Dark olivaceous to dark grayish stromata were erumpent and conspicuous on the brown lesions in the later stage of disease development. Conidiophores were simple or occasionally branched, 1- to 2-septate, pale brown to olivaceous brown, and smooth walled. Conidia (n = 30) were olivaceous brown to grayish brown, verrucose, thick-walled, mildly curved, allantoid to fusiform, one- to five-septate (mostly three-septate), and 20 to 45 × 3.5 to 5 μm. Morphological characteristics of the fungus were consistent with those of Lecanosticta acicola (Thüm.) Syd. (anamorph of Mycosphaerella dearnessii M.E. Barr), previously known as the causal agent of brown spot needle blight of pines (2,4). The teleomorph was not observed. On potato dextrose agar, single-spore cultures of three isolates were obtained from conidia sporulating on needles. An isolate was preserved at the Korean Agricultural Culture Collection (Accession No. KACC44982). Genomic DNA was extracted using the DNeasy Plant Mini DNA Extraction Kit (Qiagen Inc., Valencia, CA) and the complete internal transcribed spacer (ITS) region of rDNA was amplified and sequenced with the primers ITS1/ITS4. The resulting ITS sequence of 543 bp was deposited in GenBank (Accession No. JQ245448). A GenBank BLAST search produced an exact match for the sequences of M. dearnessii (= L. acicola) on P. mugo Tura from Lithuania (HM367708) and P. radiata D. Don from France (GU214663), with 100% sequence similarity. To conduct a pathogenicity test, a conidial suspension (approx. 2 × 105 conidia/ml) was prepared by harvesting conidia from 5-week-old cultures of KACC44982 and sprayed onto the needles of five 3-year-old healthy seedlings. Five noninoculated seedlings of the same age served as controls. Inoculated and noninoculated plants were kept in humid chambers for 48 h in a glasshouse. After 28 days, typical leaf spot symptoms started to develop on the needles of inoculated plants. The fungus, L. acicola, was reisolated from those lesions, confirming Kochs postulates. No symptoms were observed on control plants. The disease has been previously reported on several species of Pinus in the Americas (1) and recently in China (3), Japan (4), and Europe (2). To our knowledge, this is the first report of the Lecanosticta-Pinus association in Korea. Occurrence of the disease in Korea is a new threat to the health of black pine, especially in nursery plots. References: (1) D. F. Farr and A. Y. Rossman. Fungal Databases. Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved from http://nt.arsgrin.gov/fungaldatabases/ December 2011. (2) L. Jankovsky et al. Plant Protect. Sci. 45:16, 2009. (3) C. Li et al. J. Nanjing Inst. For. 1986:11, 1986. (4) Y. Suto and D. Ougi. Mycoscience 39:319, 1998.

Occurrence of Leaf Spot on Eriobotrya japonica Caused by Entomosporium mespili in Korea

Since 2008, a new leaf spot disease has been found in loquat tree (Eriobotrya japonica) at a nursery station in Goheung, Korea. Above 50% of the seedlings developed the spot symptoms on the leaves. The infected plants were generally reduced in the seedling vigour and early defoliation was occurred. The infected leaves developed grayish lesion with dark reddish brown margin. The pathogen developed round to ellipsoidal acervuli on the lesion. Based on morphological characteristics of the pathogen, the fungus was identified as Entomosporium mespili. The cultured pathogen successfully reproduced the same disease symptom on the leaves of loquat tree and found to be E. mespili. A monoconidial culture was deposited in Korean Agricultural Culture Collection (KACC 44727). This is the first report of E. mespili causing leaf spot of loquat tree in Korea.

Genotypic Characterization of Cherry Witches` Broom Pathogen Taphrina wiesneri Strains

The ascomycetous fungus Taphrina wiesneri, the pathogen of cherry witches` broom, is highly pathogenic to Prunus yedoensis, the most widely planted cherry trees in Korea as park and roadside trees. A collection of 13 strains of the pathogen in Korea and Japan was characterized by 18S rDNA gene sequence and restriction fragment length polymorphism (RFLP) analysis. In cluster analysis based on 18S rDNA gene sequence the strains were divided into 2 clusters. In RFLP analysis of the rDNA-IGS region using HhaI, the strains were separated into four patterns, B, C, D and G, of which pattern G was new.

Efficacy of Fungicides for the Control of Leaf Spots on Eriobotrya japonica and Photinia glabra

Since the late 2000s, a serious Entomosporium leaf spot disease, caused by Entomosporium mespili, has been found frequently on leaves of Eriobotrya japonica and Photinia glabra at a nursery station in Goheung and Jeju, respectively. Studies were conducted to select fungicides that would effectively control Entomosporium leaf spot. Among the three fungicides tested, weekly foliar applications of propiconazole and chlorothalonil effectively reduced disease severity on E. japonica and P. glabra showing control value of 64.1% and 87.6%, respectively. Weekly treatments of thiopanate methyl were less effective. Propiconazole controlled the disease, but, it was phytotoxic to P. glabra.

Suppression of Bacterial Wilt in Tomato Plant Using Pseudomonas putida P84

Bacterial wilt caused by Ralstonia solanacearum has become a severe problem on tomato in Korea and no effective control measures are available yet. Pseudomonas species play key roles for the biocontrol of many plant diseases especially in soil. A rhizobacterial population of 150 Pseudomonas strains, isolated from the rhizosphere soil of various plants grown at different sites, was screened for 2,4-diacetylphloroglucinol producing gene (PhlD) by PCR. Two strains (P83 and P84) among them were found to be phlD positive. When the isolates were analysed by 16S rDNA (Sensu Stricto), all isolates yielded amplified products of 1,018bp. Of the 150 isolates of Pseudomonas spp., a bacterial strain P. putida P84 isolated from tomato rhizosphere showed to suppress a wide range of phytopathogenic bacteria in vitro. The best source of carbon for P84 strain were glucose, arabinose, inositol and melibiose. In greenhouse experiments, P84 strain suppressed the development of bacterial wilt in tomato with a control value of 60%.