• Research in Plant Disease
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• v.19 no.4
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• pp.265-272
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• 2013

Totally sixty three bacteria were isolated from lower stems showing symptoms of bacterial wilt on pepper plants in 14 counties of 7 provinces, Korea. The isolates showed strong pathogenicity on red pepper (cv. Daewang) and tomato (cv. Seogwang) seedlings. All virulent bacteria were identified as Ralstonia solanacearum based on colony types, physiological and biochemical tests and polymerase chain reaction (PCR). All R. solanacearum isolates from peppers were race 1. The bacterial isolates consisted of biovar 3 (27%) and biovar 4 (73%). Based on polymorphic PCR bands generated by repetitive sequence (rep-PCR), the 63 R. solanacearum isolates were divided into 12 groups at 70% similarity level. These results will be used as basic materials for resistant breeding program and efficient control against bacterial wilt disease of pepper.

• The Plant Pathology Journal
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• v.36 no.4
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• pp.355-363
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• 2020

Bacterial traits for virulence of Ralstonia solanacearum causing lethal wilt in plants were extensively studied but are not yet fully understood. Other than the known virulence factors of Ralstonia solanacearum, this study aimed to identify the novel gene(s) contributing to bacterial virulence of R. solanacearum. Among the transposon-inserted mutants that were previously generated, we selected mutant SL341F12 strain produced exopolysaccharide equivalent to wild type strain but showed reduced virulence compared to wild type. In this mutant, a transposon was found to disrupt the murI gene encoding glutamate racemase which converts L-glutamate to D-glutamate. SL341F12 lost its motility, and its virulence in the tomato plant was markedly diminished compared to that of the wild type. The altered phenotypes of SL341F12 were restored by introducing a full-length murI gene. The expression of genes required for flagella assembly was significantly reduced in SL341F12 compared to that of the wild type or complemented strain, indicating that the loss of bacterial motility in the mutant was due to reduced flagella assembly. A dramatic reduction of the mutant population compared to its wild type was apparent in planta (i.e., root) than its wild type but not in soil and rhizosphere. This may contribute to the impaired virulence in the mutant strain. Accordingly, we concluded that murI in R. solanacearum may be involved in controlling flagella assembly and consequently, the mutation affects bacterial motility and virulence.

• Research in Plant Disease
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• v.28 no.3
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• pp.143-151
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• 2022

In order to investigate the cause of wilting symptoms in red pepper field of Korea, the frequency of occurrence of red peppers showing wilting symptoms was investigated in pepper cultivation fields in Goesan, Chungcheongbuk-do for 5 years from 2010 to 2014. There was a difference in the frequency of wilting symptoms depending on the year of investigation, but the frequency of occurrence increased as the investigation period passed from June and July to August. During this period, Ralstonia solanacearum causing the bacterial wilt was isolated at a rate four times higher than Phytophthora capsica causing the Phytophthora late blight. In wilted peppers collected in Goesan of Chungbuk and Andong of Gyeongbuk in 2013 and 2014, R. solanacearum and P. capsici were isolated from 20.3% and 3.8% of the total fields, respectively. In the year with a high rate of wilting symptoms, the average temperature was high, and the disease occurrence date of the bacterial wilt, estimated with disease forecasting model, was also fast. The inconsistency between the number of days at risk of Phytophthora late blight and the frequency of occurrence of wither symptoms is thought to be due to the generalization of the use of cultivars resistant to the Phytophthora late blight in the pepper field. In our study, the wilting symptoms were caused by the bacterial wilt caused by R. solanacearum rather than the Phytophthora late blight caused by P. capsica, which is possibly caused by increasing cultivation of pepper varieties resistant to the Phytophthora late blight in the field.

• Journal of the Korean Society of Tobacco Science
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• v.20 no.1
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• pp.66-70
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• 1998

TMV resistant lines (TRLs) originated from the Blo plant of Nicotiana tabacum cv. NC82 transformed with TMV coat protein cDNA which initially showed delayed disease symptom were selected for increased resistance in each subsequent generation. The result of field experiment of the transgenic tobacco lines in the fifth generation for TMV resistance and their response to other tobacco diseases (black shank, bacterial wilt, and powdery mildew) is described in this report. When fifteen TRLs of the fifth generation were tested for TMV resistance by mechanically inoculating the individual plants, over 95 percent of the plants of 6 lines showed complete resistance even 8 weeks after the inoculation. Average frequency of the resistant plants in TRLs of the fifth generation 8 weeks after the inoculation was 87%. Stable insertion and expression of TMV coat protein cDNA in the fifth generation of the transgenic tobacco plant were confirmed by PCR and immunoblot hybridization, respectively. All TRLs were resistant to the black shank but were susceptible to the bacterial wilt disease and the powdery mildew to the same degree as non-transgenic NC82 was. Therefore, it was indicated that the phenotypes related at least to disease resistance were not changed in the transgenic tobacco. Key words : TMV CP cDNA, TMV resistant tobacco plant, transformation.

• Research in Plant Disease
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• v.16 no.3
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• pp.290-293
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• 2010

Bacterial canker, caused by Clavibacter michiganensis subsp. michiganensis, is a very damaging disease to tomato (Lycopersicon esculentum) farm in Korea. It infects tomato, spreads through the xylem and causes bacterial wilt and canker. Selection of resistant cultivar is the best way to prevent or reduce the occurrence of the disease. Thirty-nine tomato cultivars, twenty-one cherry tomato cultivars and thirteen rootstock tomato cultivars were inoculated with Clavibacter michiganensis subsp. michiganensis, to evaluate tomato cultivarspecific resistance against bacterial canker. In the evaluation of 73 major commercial cultivars, 'Sunmyung', 'Sweet', 'Akiko', 'Dadaki', 'Match', 'Magnet', 'Friend', and 'Greenpower' were found to have a high level of resistance to bacterial canker of tomatoes.

• The Korean Journal of Pesticide Science
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• v.13 no.1
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• pp.45-53
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• 2009

An antagonistic bacterial strain KLF01 was isolated from rhizosphere of tomato and identified to be Lactobacillus sp. by biochemical and genetic analysis. This strain showed antagonism against the used plant pathogenic bacteria like Ralstonia solanacearum, (bacterial wilt), Xanthomonas axonopodis pv. citri, (Citrus canker), Xanthomonas campestris pv. vesicatoria (Bacterial spot), Eriwinia pyrifoliae (Shoot-blight) and Eriwinia carotovora subsp. carotovora group (Potato scab) through agar well diffusion method. In planta test done by drench application of strain KLF01 $(4{\times}10^8 cfu/ml)$ into the experimental plot containing tomato (Solanum lycopersicum L.) cultivar 'Lokkusanmaru' and red pepper (Capsicum annuum L.) cultivar 'Buja' plants, in pot test post-inoculated with the plant pathogenic bacteria, R. solanacearum significantly reduced the disease severity, compared to the non-treated plants.

• 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.

• Research in Plant Disease
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• v.18 no.4
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• pp.361-369
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• 2012

A population density model for bacterial wilt, which is caused by Ralstonia solanacearum, in hot pepper was developed to estimate the primary infection date after overwintering in the field. We developed the model mechansitically to predict reproduction of the pathogen and pathogensis on seedlings of the host. The model estimates the pathogen's populations both in the soil and in the host. In order to quantify environmental infection factors, various temperatures and initial population densities were determined for wilt symptoms on the seedlings of hot pepper in a chamber. Once, the pathogens living in soil multiply up to 400 cells/g of soil, they can infect successfully in the host. Primary infection in a host was supposed to be started when the population of the pathogen were over $10^9$ cells/g of root tissue. The estimated primary infection dates of bacterial wilt in 2011 in Korea were mostly mid-July or late-July which were 10-15 days earlier than those in 2010. Two kinds of meterological data, synoptic observation and field measurements from paddy field and orchard in Kyunggi, were operated the model for comparing the result dates. About 1-3 days were earlier from field data than from synoptic observation.

• The Plant Pathology Journal
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• v.32 no.1
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• pp.25-32
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• 2016

Potato is one of the most important crops worldwide. Its commercial cultivars are highly susceptible to many fungal and bacterial diseases. Among these, bacterial wilt caused by Ralstonia solanacearum causes significant yield loss. In the present study, integrated proteomics and genomics approaches were used in order to identify bacterial wilt resistant genes from Rs resistance potato cultivar CT-206-10. 2-DE and MALDI-TOF/TOF-MS analysis identified eight differentially abundant proteins including glycine-rich RNA binding protein (GRP), tomato stress induced-1 (TSI-1) protein, pathogenesis-related (STH-2) protein and pentatricopeptide repeat containing (PPR) protein in response to Rs infection. Further, semi-quantitative RT-PCR identified up-regulation in transcript levels of all these genes upon Rs infection. Taken together, our results showed the involvement of the identified proteins in the Rs stress tolerance in potato. In the future, it would be interesting to raise the transgenic plants to further validate their involvement in resistance against Rs in potato.

• Korean Journal Plant Pathology
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• v.2 no.2
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• pp.114-120
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• 1986

Significant reduction in disease severity of bacterial wilt (Pseudomonas solanacearum) on the susceptible tobacco cultivar BY 4 was observed until mid-July in a naturally infested field when bacterial suspensions of avirulent isolate were applied to tobacco root zones at one day before and fourty days after transplanting into the field. However, rapid increase in disease severity after mid-July resulted in the same severity $(70\%)$ as on cultivar BY 4 without the application of the avirulent bacterial suspension at the end of the season. Yield increase in cultivar BY 4 was $35\%$ due to the treatment, resulting in $10\%$ price increase. The suppression me chanism did not appear to be dependent upon the inhibition of the virulent bacterial multiplication by the avirulent bacteria in tobacco rhizosphere soil because of no significant difference in the density of the patho genic bacteria between treated and untreated plant root zones. However. penetration of the virulent bacteria into the root systems and their multiplication in tobacco stem were inhibited remarkably by preinoculation with avirulent one, suggesting that those are related to the suppression of disease incidence.