• 한국균학회소식:학술대회논문집
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• 2015.05a
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• pp.54-54
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• 2015

Crops lack genetic resistance to most necrotrophic soil-borne pathogens and parasitic nematodes that are ubiquitous in agroecosystems worldwide. To overcome this disadvantage, plants recruit and nurture specific group of antagonistic microorganisms from the soil microbiome to defend their roots against pathogens and other pests. The best example of this microbe-based defense of roots is observed in disease-suppressive soils in which the suppressiveness is induced by continuously growing crops that are susceptible to a pathogen. Suppressive soils occur globally yet the microbial basis of most is still poorly described. Fusarium wilt, caused by Fusarium oxysporum f. sp. fragariae is a major disease of strawberry and is naturally suppressed in Korean fields that have undergone continuous strawberry monoculture. Here we show that members of the genus Streptomyces are the specific bacterial components of the microbiome responsible for the suppressiveness that controls Fusarium wilt of strawberry. Furthermore, genome sequencing revealed that Streptomyces griseus, which produces a novel thiopetide antibiotic, is the principal species involved in the suppressiveness. Finally, chemical-genetic studies demonstrated that S. griseus antagonizes F. oxysporum by interfering with fungal cell wall synthesis. An attack by F. oxysporum initiates a defensive "cry for help" by strawberry root and the mustering of microbial defenses led by Streptomyces. These results provide a model for future studies to elucidate the basis of microbially-based defense systems and soil suppressiveness from the field to the molecular level.

• Journal of Microbiology and Biotechnology
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• v.19 no.8
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• pp.760-764
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• 2009

In this study, we investigated the antifungal activity of three different forms of silver nanoparticles against the unidentified ambrosia fungus Raffaelea sp., which has been responsible for the mortality of a large number of oak trees in Korea. Growth of fungi in the presence of silver nanoparticles was significantly inhibited in a dose-dependent manner. We also assessed the effectiveness of combining the different forms of nanoparticles. Microscopic observation revealed that silver nanoparticles caused detrimental effects not only on fungal hyphae but also on conidial germination.

• Journal of Microbiology and Biotechnology
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• v.17 no.11
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• pp.1765-1771
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• 2007

A polymerase chain reaction (PCR)-based method was developed to detect the DNA of Ralstonia solanacearum, the causal agent of bacterial wilt in various crop plants. One pair of primers (RALSF and RALSR), designed using cytochrome c1 signal peptide sequences specific to R. solanacearum, produced a PCR product of 932 bp from 13 isolates of R. solanacearum from several countries. The primer specificity was then tested using DNA from 21 isolates of Ralstonia, Pseudomonas, Burkholderia, Xanthomonas, and Fusarium oxysporum f. sp. dianthi. The specificity of the cytochrome c1 signal peptide sequences in R. solanacearum was further confirmed by a DNA-dot blot analysis. Moreover, the primer pair was able to detect the pathogen in artificially inoculated soil and tomato plants. Therefore, the present results indicate that the primer pair can be effectively used for the detection of R. solanacearum in soil and host plants.

• Research in Plant Disease
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• v.22 no.4
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• pp.236-242
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• 2016

Bacterial wilt caused by Ralstonia solanacearum is one of the most devastating diseases in major Solanaceae crops. The pathogen is easily disseminated and survives for many years in plant farming system. Although chemicals are applied to control the disease, they are of limited efficacy and cause several problems. Therefore, the use of phage therapy has been suggested to control the disease as a biological agent. In this study, we discovered bacteriophages lysing diverse Ralstonia isolates from plant and soil samples obtained from the potato cultivated field in Jeju. Three times repeated pickings of plaques resulted in obtaining 173 single phages showing diverse spectrum of host-specificity. With the results, 12 core phages were selected and dendrogram was generated. Genetic diversity of the selected phages was also confirmed by AFLP (Amplified Fragment of Length Polymorphism) fingerprinting. The stability of the phages was investigated in various temperatures and various conditions of pH in vitro. The phages were stable at $16^{\circ}C-44^{\circ}C$ and pH 6-10. Morphological characterization of the phages revealed they were all classified into the Podoviridae, but had diverse head sizes. The results of this research will contribute to control the disease and further researches regarding genetic and molecular aspects will facilitate understanding phage and bacteria interaction.

• Journal of Microbiology and Biotechnology
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• v.14 no.1
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• pp.212-215
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• 2004

In order to develop a biocontrol agent that can effectively control Fusarium wilt on Cymbidium genus, the effectiveness of antagonistic microbes against the cause pathogen was screened. The selected microbe showed a broad spectrum of antifungal activity, and the culture broth of this microbe had better preventive effect on Fusarium wilt than the commercial chemical agent in the pot assay. This isolated strain, GBA-12, was identified as Streptomyces kasugaensis, and the antifungal substance was purified from a broth culture of GBA-12. This purified substance was identified as a polyene macrolide (YS-822A) that was newly discovered from Streptomyces kasugaensis, and it exhibited antifungal activity against several phytopathogenic fungi.

• The Plant Pathology Journal
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• v.38 no.2
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• pp.131-145
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• 2022

Ceratocystis wilt disease has caused significant mortality in duku (Lansium domesticum) since 2014 and has now spread to all districts in South Sumatra, Indonesia. Recently, 16 isolates from duku representing populations from various districts in South Sumatra were isolated. Analysis for the morphological characteristic of the isolate showed that the population has a uniform morphology. Genetic analysis based on internal transcribed spacer (ITS) and β-tubulin sequences verified that the population has being dominated by the ITS5 haplotype of Ceratocystis fimbriata and a new ITS group, the ITS7b haplotype that was localized in Musi Banyuasin. Both haplotypes were highly pathogenic to duku. Inoculation tests on various forest and agroforestry plant hosts showed that both haplotypes were highly pathogenic to Acacia mangium, moderately pathogenic to Acacia carsicarpa, Eucalyptus urophylla, and Melaleuca cajuputi, but weakly pathogenic to Dyera costulata, Hevea brasiliensis, and Alstonia scholaris. Therefore, this pathogen becomes a serious threat to Indonesia's biodiversity due to its ability to infect forest and agroforestry plants, especially the indigenous ones.

• The Korean Journal of Pesticide Science
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• v.19 no.3
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• pp.323-328
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• 2015

Control efficacy was investigated with fungicides as 3 copper compound, 3 antibiotic fungicides and one fungicide containing to quinolone against the growth of Ralstonia solanacearum on NA medium and the disease occurrence on pepper seedlings. Among 7 fungicides, oxytetracycline was shown the highest activity against a growth of the pathogen in the agar diffusion method, but validamycin showed no activity against the pathogen. With $1000{\mu}g\;mL^{-1}$ of each copper fungicide as copper hydroxide, copper oxychloride+ dithianone and copper sulfate, 2.2, 1.3 and 1.5 mm in size of clear zone only could be found, respectively. In pepper seedling test, oxytetracycline showed a perfect activity in all treatments 7 days after inoculation. However, its activity was decreased from $500{\mu}g\;mL^{-1}$ of treatment over the time. Copper fungicides showed the control efficacy lower than antibiotic fungicides except for validamycin. Based on the results, it was suggested that it would be better to use antibiotic fungicides than copper fungicides to control pepper bacterial wilt in the fields.

• The Korean Journal of Mycology
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• v.25 no.1 s.80
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• pp.10-19
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• 1997

Fusarium wilt of radish (Raphanus sativus L.) is caused by the Fusarium oxysporum f. sp. raphani (FOR) which mainly attacks Raphanus spp. The pathogen is a soil-borne and forms chlamydospores in infected plant residues in soil. Infected pathogen colonizes the vascular tissue, leading to necrosis of the vascular tissue. Growth promoting beneficial organisms such as Pseudomonas fluorescens WCS374 (strain WCS374), P. putida RE10 (strain RE10) and Pseudomonas sp. EN415 (strain EN415) were used for microorganisms-mediated induction of systemic resistance in radish against Fusarium wilt. In this bioassy, the pathogens and bacteria were treated into soil separately or concurrently, and mixed the bacteria with the different level of combination. Significant suppression of the disease by bacterial treatments was generally observed in pot bioassy. The disease incidence of the control recorded 46.5% in the internal observation and 21.1% in the external observation, respectively. The disease incidence of P. putida RE10 recorded 12.2% in the internal observation and 7.8% in the external observation, respectively. However, the disease incidence of P. fluorescens WCS374 which was proved to be highly suppressive to Fusarium wilt indicated 45.6% in the internal observation and 27.8% in the external observation, respectively. The disease incidence of P. putida RE10 mixed with P. fluorescens WCS374 or Pseudomonas sp. EN415 was in the range of 10.0-22.1%. On the other hand, the disease incidence of P. putida RE10 mixed with Pseudomonas sp. EN415 was in the range of 7.8-20.2%. The colonization by FOR was observed in the range of $2.4-5.1{\times}10^3/g$ on the root surface and $0.7-1.3{\times}10^3/g$ in the soil, but the numbers were not statistically different. As compared with $3.8{\times}10^3/g$ root of the control, the colonization of infested ROR indicated $2.9{\times}10^3/g$ root in separate treatments of P. putida RE10, and less than $3.8{\times}10^3/g$ root of the control. Also, the colonization of FOR recorded $5.1{\times}10^3/g$ root in mixed treatments of 3 bacterial strains such as P. putida RE10, P. fluorescens WCS374 and Pseudomonas sp. EN415. The colonization of FOR in soil was less than that of FOR in root part. Based on soil or root part, the colonization of ROR didn't indicate a significant difference. The colonization of introduced 3 fluorescent pseudomonads was observed in the range of $2.3-4.0{\times}10^7/g$ in the root surface and $0.9-1.8{\times}10^7/g$ in soil, but the bacterial densities were significantly different. When growth promoting organisms were introduced into the soil, the population of Pseudomonas sp. in the root part treated with P. putida RE10 was similar in number to the control and recorded the low numerical value as compared with any other treatments. The population density of Pseudomonas sp. in the treatment of P. putida RE10 indicated significant differences in the root part, but didn't show significant differences in soil. The population densities of infested FOR and introduced bacteria on the root were high in contrast to those of soil. P. putida RE10 and Pseudomonas sp. EN415 used in this experiment appeared to induce the resistance of the host against Fusarium wilt.

• Research in Plant Disease
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• v.16 no.2
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• pp.148-152
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• 2010

To establish the efficient screening method for resistance of radish to F. oxysporum f. sp. raphani, we investigated the development of Fusarium wilt of two radish cultivars, 'Songbaek' (susceptible) and 'Tokwang' (moderately resistant), according to several conditions such as inoculation methods, inoculum concentrations, and dipping periods of radish roots in spore suspension. By infected soil and soil-drenching inoculation methods, Fusarium wilt did not occur on the seedlings of both cultivars. In root dipping inoculation method using cut or non-cut roots of radish plants, the cut roots were easily infected by the pathogen than non-cut roots. And the disease development of two cultivars represented significant difference in non-cut root method. On the other hand, disease severity of Fusarium wilt on radish seedlings according to inoculum concentration increased in a dose-dependant manner, regardless of dipping periods. Using screening method established from the results, the 41 commercial radish cultivars were evaluated the degree of resistance to F. oxysporum f. sp. raphani. Among them, 6 radish cultivars were resistant, 22 cultivars were moderately resistant, and 13 cultivars were susceptible to Fusarium wilt.

• Journal of Bio-Environment Control
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• v.28 no.3
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• pp.212-217
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• 2019

Bacterial wilt caused by Ralstonia solanacearum is a major disease that affects tomato plants widely. R. solanacearum is a soil born pathogen which limits the disease control measures. Therefore, breeding of resistant tomato variety to this disease is important. To identify the susceptible variety, degree of disease resistance has to be determined. In this study, micro sap flow sensor is used for accurate prediction of resistant degree. The sensor is designed to measure sap flow and water use in stems of plants. Using this sensor, the susceptibility to bacterial wilt disease can be identified two to three days prior to the onsite of symptoms after innoculation of R. solanacearum. Thus, this find of diagnosis approach can be utilized for the early detection of bacterial wilt disease.