Shoji Ohga’s research while affiliated with Kyushu University and other places

In 2016, the typical symptoms of rust disease were observed on rough fleabane (Erigeron strigosus Muhl., Asteraceae) in Yongin-si, Korea. The diseased leaves were covered with yellow spots and chlorosis, and massive urediniospores covered the entire plant. Subsequently, a severe infection resulted in leaf blight and defoliation. To investigate the rust disease on rough fleabane, observations were conducted by using stereo microscopy, light microscopy, and scanning electron microscopy. The observations showed that the urediniospores were subglobose to polygonal and 20.4-32.3 × 14.7-23.6μm in size and the teliospores were septate, obovoid to ellipsoid, and 72.1-85.1 X 21.0-24.0μm in size. The phylogenetic analysis based on partial 28S rDNA sequences indicated that it was closely related to Coleosporium asterum (AF426241) isolated from Aster sp. Based on the results of the morphological and phylogenetic analyses, this is thought to be the first report of C. asterum as a causative agent of rust disease on rough fleabane in Korea.

The present study reports the morphological and phylogenetic characteristics of Tyrophagus putrescentiae from Hypsizygus marmoreus in Korea. This species is morphologically characterized by two pigmented eyespots on the prodorsal shield, concave posterior margin of coxal plate n, prominently and api- cally enlarged supracoxal seta shaft at bases of pectinations, and solenidion omegal on tarsi I and n, respectively and length of setae dl compared to setae cl and setae d2. The internal transcribed spacer 2 (ITS2) in the ribosomal DNA (rDNA), which is reliable for species identification, and the cytochrome oxidase sub- unit I (COl) in the mitochondrial DNA, which is a highly conserved region in eukaryotes, were sequenced. The resulting phylogenetic trees for COI and ITS2 apparently showed that the tested samples in this study were clustered with T. putrescentiae and separated from other species in the genus. This research would be useful for controlling mites from H. marmoreus in Korea and could help improve the quality and quantity of H. marmoreus production.

Fuel moisture contents in the forest floor are one of important factors for forest fire spread due to their role as a possible fire ignition and are closely related to changes in weather factors. In the present study, we analyzed changes in forest fuel moisture content for two tree species (Pinus densijlora and Quercus dentata) associated with two different weather measurement data (in-situ measurement within the forest and observation at the weather station) during three consecutive years of monitoring including the Korean forest fire danger seasons (spring and fall). Results showed that the weather data from in-situ measurement within the forest and the CWS (Chuncheon Weather Station) had different patterns in that average temperature and max temperature tended to be higher in the forest, while min temperature had lower in the forest. These different patterns in weather factors affected the dead forest fuel moisture content thereby causing differences in the forest fuel moisture content among species. Results also revealed significant relation between precipitation and forest fuel moisture content indicating forest fuel moisture content decreases significantly after precipitation events during both seasons. The present study suggests that weather data within the forest which can reflect regional weather characteristics must be acquired to more accurately determine the forest fuel moisture content. Especially in Korea where most of the land consists mainly mountainous forestland. Hence, it is necessary to conduct future research which comprises comparative analysis of various leaf types based on dynamic changes of in-situ weather factors within the forest and monitor precise moisture content changes by leaf type after precipitation in order to ensure the accuracy of forest fire prediction systems during the forest fire danger season.

In this study, we developed a nested PCR detection method based on draft genomic sequences of Mycosphaerella nawae and then applied the method to survey primary symptoms of circular leaf spot (CLS) and the seasonal ascospore scattering period. To develop the assay for detecting the fungus, 11 primers for the initial PCR and 19 primers for the nested PCR were designed (based on the glycoside hydrolase family 3 gene) using draft genomic sequences of M. nawae. Consequently, the primer pairs Mn-Fl/ Mn-Rl and Mn-nes-168f/Mn-nes-483r were selected and their specificities examined using regional M. nawae isolates, various healthy persimmon leaves, other fungal pathogens of persimmon, and allied species of M. nawae. Furthermore, the developed nested PCR method was applied for the diagnosis of the initial stage of CLS using both diseased and asymptomatic leaves. Additionally, scattered M. naivae ascospores collected by a spore sampler were surveyed from May to November 2015. Therefore, it is assumed that the nested PCR method can suggest the proper fungicide spraying period for CLS through anticipation of the ascospore quantity, and the early diagnosis of CLS will enable control of its development on persimmon.

Gray mold neck rot was observed on onion bulbs (Allium cepa L.) in low-temperature warehouses in Changnyeong-gun, Korea. The causative pathogen was isolated from rotted onion bulb lesions and identified as Botrytis aclada based on morphological and culture characteristics, the sequences of three nuclear genes (G8PDH, HSP60, and RPBZ), and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) for Botrytis spp. identification. Although onion gray mold disease caused by B. allii, B. cinerea, and B. squamosa species has previously been reported in Korea, this, to the best of our knowledge, is the first report of B. aclada causing gray mold neck rot disease of onion bulbs in Korea.

Hypsizygus marmoreus is an edible and medicinal mushroom belongs to Basidiomycetes. The optimal culture conditions for the vegetative growth of brown and white strains of H. marmoreus were investigated to obtain suitable farming condition. Temperature suitable and unsuitable for vegetative growth was obtained at 20 and 35°C, respectively. The both strains of H. mermoreus love medium temperature and the mycelial growth was well developed at 20-25°C. This mushroom prefer pH ranging 6-8 for mycelial growth. The highest and lowest mycelial growth was found at pH 7 and 5 of both strains, respectively. Among 5 different carbon sources, sucrose was the best, whereas, maltose and lactose were the worst. The most suitable nitrogen sources were CaNO, (in brown strain 65.6 mm and in white strain 56.3 mm) and the most unsuitable was NH4HPO4 (in brown strain 44.02 mm and in white strain 40.2 mm). Five different culture media were used to screen the optimal mycelial growth of H. marmoreus. PDA and YM (yeast-malt extract) were the most suitable and Czapek dox and Hennerberg were the most unfavorable for vegetative growth, whereas, glucose peptone was moderately suitable. The highest and lowest vegetative growth was observed in media prepared with mango (Mangifera indica) and koroi (Albizia procera) sawdust, respectively. However, for both strains, 3 weeks were required to complete mycelium running in mango sawdust, whereas, 4 weeks were spent to get 100% mycelium running in mahagoni (Swietenia mahagoni) and koroi sawdust. The premordia and fruiting bodies of H. marmoreus were formed in the mango sawdust medium sooner. The fruiting bodies of brown strain were formed earlier than white strain after occurrence of primordia. In case of limiting ventilation, the stem development was found to be good but no cap was seen to be formed. Ventilation influenced the growth and development of fruit body of H. marmoreus. Therefore, it could be said that physiochemical requirement for the vegetative growth is strictly considerable and results focused in this paper could be followed by farmers to scale up farming of H. marmoreus in Bangladesh.