Young-Jin Koh

Bactericidal activity and water purification of immobilized TiO2 photocatalyst in bean sprout cultivation

Immobilized TiO2 photocatalysts were used to sterilize and reclaim the wastewater of bean sprout cultivation from a continuous hydro-circulation system. The photocatalysts effectively killed bacteria and degraded organic pollutants in the wastewater. Stimulation of bean sprout growth and suppression of decaying pathogens were also induced by the TiO2 photocatalytic activity.

Outbreak of bacterial canker on Hort16A (Actinidia chinensis Planchon) caused by Pseudomonas syringae pv. actinidiae in Korea

Abstract Bacterial canker was first observed on the kiwifruit cv. ‘Hort16A (Actinidia chinensis)’ in Jeju Province, Korea, in spring 2006. Die back or blight on young canes, often with red-rusty exudation on canes or trunks, and dark brown irregular spots surrounded with yellowish halos on leaves are the typical symptoms. These symptoms closely resemble those caused by Pseudomonas syringae pv. actinidiae on the kiwifruit cv. ‘Hayward (Actinidia deliciosa)’. A sudden outbreak and rapid spread of the bacterial canker resulted in the death of severely infected vines and eradication of completely devastated orchards of the kiwifruit cv. ‘Hort16A’. Contaminated pruning shears and climatic conditions appear to have been responsible for the sudden outbreak and rapid spread of the epidemics on the kiwifruit cv. ‘Hort16A’ vines. The causal bacterium was isolated from diseased vines of the kiwifruit cv. ‘Hort16A’ and identified as P. syringae pv. actinidiae, which is the same bacterial pathogen responsible for cankers on the kiwifruit cv. ‘Hayward’ by morphological, cultural, physiological and biochemical, molecular and pathogenicity analyses.

Bacillus subtilis S1-0210 as a Biocontrol Agent against Botrytis cinerea in Strawberries

Bacillus subtilis S1-0210 was selected as a biological agent against Botrytis cinerea in strawberry. The isolate inhibited mycelial growth of B. cinerea in vitro tests. A wettable powder formulation of B. subtilis S1-0210 significantly reduced infection rates with lower than 5%, compared with higher than 70% of infection rates in untreated control. The formulation showed 85 to 89% control efficacies of gray mold incidences on fruits of strawberry in pots. Pre-treatment of the agent was more effective in controlling gray mold on fruits and leaves than post-treatment at the early stage of disease development. The formulation also showed 70% control efficacy of gray mold incidence on fruits of strawberry in a field trial. The results indicate that B. subtilis S1-0210 in the wettable powder formulation may be a potential biocontrol agent to control gray mold on strawberry.

Antifungal Activity of Lichen-forming Fungi against Colletotrichum acutatum on Hot Pepper

Antifungal activity of Korean and Chinese lichen-forming fungi (LFF) was evaluated against plant pathogenic fungus of Colletotrichum acutatum, causal agent of anthracnose on hot pepper. This is the first attempt to evaluate antifungal activity of LFF, instead of lichen thalli, against C. acutatum. Total 100 LFF were isolated from the lichens with discharged spore method or tissue culture method. Among the 100 isolates, 8 LFF showed more than 50% of inhibition rates of mycelial growth of the target pathogen. Especially, Lecanora argentata was highly effective in inhibition of mycelial growth of C. accutatum at the rate of 68%. Antifungal activity of other LFF was in the order of Cetrelia japonica (61.4%), Ramalina conduplicans (59.5%), Umbilicaria esculenta (59.5%), Ramalina litoralis (56.7%), Cetrelia braunsiana (56.5%), Nephromopsis pallescensn (56.1%), and Parmelia simplicior (53.8%). Among the tested LFF, 61 isolates of LFF exhibited moderate antifungal activity against the target pathogen at the inhibition rates from 30 to 50%. Antifungal activity of the LFF against C. acutatum was variable at the species level rather than genus level of LFF. This study suggests that LFF can be served as a promising bioresource to develop novel biofungicides.

Comparative Analysis of Korean and Japanese Strains of Pseudomonas syringae pv. actinidiae Causing Bacterial Canker of Kiwifruit

Genomic and phenotypic characteristics of the bacterial strains of Pseudomonas syringae pv. actinidiae and P. syringae pv. syringae collected from several kiwifruit orchards of Korea were investigated and compared with those from Japan to elucidate their phylogenic relationships. All the strains of P. syringae pv. actinidiae and pv. syringae tested were sensitive to copper sulfate but Korean and Japanese strains showed quite different responses to streptomycin. Korean strains were sensitive to streptomycin, but most of the Japanese strains of P. syringae pv. actinidiae were highly resistant to streptomycin. Japanese strains were also relatively more resistant to oxytetracycline than Korean strains. Plasmid profiles were not valuable to distinguish Korean strains of P. syringae pv. actinidiae frombJapanese strains. One or more indigenous plasmids with more than 15 kb in size were detected in all strains of P. syringae pv. actinidiae, but the number and sizes of plasmids harbored in P. syringae pv. actinidiae were variable among the strains regardless of their geographic origins. There also observed no significant relationship among resistance levels of the strains of P. syringae pv. actinidiae to antibiotics, their pathogenicity and plasmid profiles. RAPD profiles were useful to analyze the strains of P. syringae pv. actinidiae and pv. syringae. All the strains of P. syringae pv. actinidiae fell into a wide cluster separated from the strains of P. syringae pv. syringae, but Korean strains of P. syringae pv. actinidiae were separated from Japanese strains. The results support that Korean and Japanese strains of P. syringae pv. actinidiae may have different phylogenic origins.

Pectobacterium carotovorum subsp. actinidiae subsp. nov., a new bacterial pathogen causing canker-like symptoms in yellow kiwifruit, Actinidia chinensis

Abstract In this study, symptoms closely resembling those caused by Pseudomonas syringae pv. actinidiae were found in kiwifruit plants (Actinidia chinensis cv. Hort16A) growing in Jeju province, Korea. Bacterial strains including strain KKH3T were isolated from representative lesions on kiwifruit plants. Comparative 16S rRNA gene sequence-based phylogenetic analysis placed these bacteria in a separate cluster within the genus Pectobacterium. Strain KKH3T showed the highest similarity (98.7%) to the recognised bacteria Pectobacterium carotovorum subsp. carotovorum and Pectobacterium wasabiae. To justify subspecies level differentiation, the partial nucleotide sequences of atpD, carA and recA from strain KKH3T were compared with those from other members of the family Enterobacteriaceae. Distant relationships between strain KKH3T and six reference strains of Pectobacterium spp. were evident in the phylogenetic tree. The results of the DNA–DNA hybridisation and polyphasic analysis revealed that strain KKH3T belongs to another subspecies of P. carotovorum, for which the name Pectobacterium carotovorum subsp. actinidiae subsp. nov. is hereby proposed.

Antifungal Activity of Lichen-Forming Fungi Isolated from Korean and Chinese Lichen Species Against Plant Pathogenic Fungi

Antifungal activity of Korean and Chinese lichen-forming fungi(LFF) was evaluated against plant pathogenic fungi of Botryosphaeria dothidea, Botrytis cinerea, Diaporthe actinidiae, Pestalotiopsis longiseta, Pythium sp., Rhizoctonia solani, and Sclerotium cepivorum. The LFF were isolated from Cladonia scabriuscula, Melanelia sp., Nephromopsis asahinae, Nephromopsis pallescens, Parmelia laevior, Pertusaria sp., Ramalina conduplicans, Ramalina sinensis, Ramalina sp., Umbilicaria proboscidea and Vulpicida sp. with discharged spore method. The isolates were deposited in the herbarium of Korean Lichen Research Institute(KoLRI) in Sunchon National University. The LFF of Melanelia sp., P. laevior, Pertusaria sp., R. conduplican and Ramalina sp. exhibited strong antifungal activity against all of the pathogenic fungi examined. Among them, LFF of P. laevior showed more than 90% of inhibition in fungal hyphae growth, compared with control. The results imply that LFF can be served as a promising bioresource to develop novel biofungicides. Mass cultivation of the LFF is now under progress in laboratory conditions for chemical identification of antifungal substances.

Botrysphaeria dothidea, the Causal Organism of Ripe Rot of Kiwifruit (Actinidia deliciosa) in Korea

Ripe rot was commonly found in overripe kiwifruits (Actinidia deliciosa) during a disease survey conducted in Jeju and Jeonnam provinces in Korea in 1999. While the disease did not manifest any clear external symptoms on kiwifruits, it caused portion of the fruit surface to collapse. Watersoaked flesh tissue could be seen on the sunken part when the skin of the collapsed portion was peeled off. The milky internal symptom with dark green margin developed concentrically as the fruit ripened. A species of Botryosphaeria was consistently isolated from lesions showing typical symptoms of ripe rot on kiwifruit, and its pathogenicity was confirmed by artificial inoculation test on healthy kiwifruits. The fungus was also pathogenic to apple and pear. The mycological characteristics of the fungus were consistent with those of Botryosphaeria dothidea. This is the first report on the detailed mycological characteristics of the causal organism of post-harvest ripe rot of kiwifruit in Korea.

Fusarium Wilt of Winter Daphne (Daphne odora Thunb.) Caused by Fusarium oxysporum

Severe wilt disease epidemic was found on winter daphnes (Daphne odora Thunb.) cultivated in farmers, nurseries in Suncheon, Jeonnam in 2003. Typical symptoms appeared on the leaves of winter daphne as yellowish wilts and turned brown from the lower leaves on the same plant. Severely infected leaves were defoliated, resulting in blight of stems and eventual death of the entire plant. Black decayed vascular tissues were distinctly observed in a wilted plant. Fusarium sp. was isolated from the diseased plants repeatedly and its pathogenicity was confirmed by artificial inoculation on healthy plants. The fungus was identified as Fusarium oxysporum on the basis of the morphological and cultural characteristics on potato dextrose agar and carnation leaf agar. The optimum temperature for fungal growth was around and the fungal growth was inhibited by metconazole, triflumizole and trifloxystrobin on potato dextrose agar. This is the first report on the wilt disease of winter daphnes caused by F.oxysporum in Korea.

Report on the Lichen List of North Korea

Total 222 lichen specimens of North Korea including 23 family, 54 genera and 119 species were newly obtained from the Hungarian Natural History Museum for the last 3 years. Among them, 12 species were added to Korean lichen checklist as new. All the species were deposited at the herbarium of Korea National Arboretum. In addition, unpublished list of lichen species distributed in Mt. Myohang was kindly donated from the Hungarian Natural History Museum. The list was originally prepared by North Korean lichenologists and kept in the museum from 1988. In the list, 26 family, 57 genera and 179 species of lichens were described and 17 species were included as new reports. This list provided 29 lichen species as new to the Korean Peninsula. This information will make significant contribution to lichenological study in the Korean Peninsula.