• The Plant Pathology Journal
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• v.26 no.1
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• pp.63-69
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• 2010

The effect of Acibenzolar-S-methyl (ASM) and Rahnella aquatilis Ra39 against apple fire blight disease caused by Erwinia amylovora were tested as a possible alternative to streptomycin. In vitro studies, no inhibition effect against the pathogen was found when ASM was tested. Under greenhouse conditions, application of R. aquatilis Ra39 with the highly susceptible M26 rootstock resulted in a marked disease suppression. Application of ASM and strain Ra39 caused a high decrease of the disease, 82% and 58% respectively; this was correlated with a reduction of the growth of the pathogen within host plants up to 64% and 49.5% respectively. Further studies in the field under artificial infection condition during full bloom revealed that application of ASM and R. aquatilis Ra39 with Gala variety resulted in a control effect up to 21 and 29% respectively. In physiological studies, enhanced activities of PR-proteins (chitinase and $\beta$-1, 3-glucanase) were detected, which are well known as biochemical markers for systemic acquired resistance. Application of ASM to apple shoots caused the highest chitinase activity followed by strain Ra39. The enzyme activity was increased after 2, 4 and 6 days from application. In addition, ASM-treatment caused the higher $\beta$-1, 3-glucanase activity than strain Ra39. Maximum enzyme activity was recorded after 6 days from application and then decreased after 8 and 10 days from application.

• The Plant Pathology Journal
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• v.38 no.5
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• pp.482-489
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• 2022

Fire blight caused by Erwinia amylovora (Ea) is a devastating disease in apple and pear trees. Oxolinic acid (OA), a quinolone family antibiotic that inhibits DNA gyrase, has been employed to control fire blight in South Korea since 2015. The continuous use of this bactericide has resulted in the emergence of OA-resistant strains in bacterial pathogens in other countries. To investigate the occurrence of OA-resistant Ea strains in South Korea, we collected a total of 516 Ea isolates from diseased apple and pear trees in 2020-2021 and assessed their sensitivities to OA. We found that all isolates were susceptible to OA. To explore the possibility of emerging OA-resistant Ea by continuous application of OA, we exposed Ea stains to a range of OA concentrations and constructed OA-resistant mutant strains. Resistance was associated with mutations in the GyrA at codons 81 and 83, which result in glycine to cysteine and serine to arginine amino acid substitutions, respectively. The in vitro growth of the mutants in nutrient media and their virulence in immature apple fruits were lower than those of wild-type. Our results suggest that OA-resistance decreases the fitness of Ea. Future work should clarify the mechanisms by which OA-resistance decreases virulence of this plant pathogen. Continuous monitoring of OA-resistance in Ea is required to maintain the efficacy of this potent bactericide.

• Korean Journal of Environmental Agriculture
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• v.42 no.4
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• pp.297-310
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• 2023

M.7 rootstock is moderately resistant to fire blight. However, M.7 is generally too vigorous for high-density apple systems, but it can be grafted onto cultivars that exhibit weak tree growth, such as 'Sansa'. This study investigated the vegetative growth, yield, and fruit quality of 'Sansa' apple trees grafted on M.7 or M.9 rootstocks to assess the feasibility of establishing domestic high-density apple systems using M.7 and to determine the optimum exposure length for rootstocks. Trees were planted with exposed rootstock lengths of 5, 10, and 15 cm. The vegetative growth of apple trees grafted onto M.7 was greater than that of M.9 and vegetative growth tended to decrease as the exposed length of rootstock increased. However, the differences in yield per tree, average weights, soluble solids contents, and titratable acidity due to the rootstock and its exposure length varied. The accumulated yield over a 10 year period and the yield efficiency of M.7 were lower than that of M.9 and the yield efficiency tended to decrease as the exposed length of rootstock increased. When apple trees were grafted onto M.9, biennial bearing and tree vigor weakening occurred if the exposed length of the rootstock was over 10 cm. Conversely, when apple trees were grafted onto M.7, vegetative growth was excessive if the exposed length of rootstock was below 10 cm. Based on the results from this study, the optimum M.7 and M.9 exposure lengths for 'Sansa' were 15 cm and 5 cm, respectively.

• Research in Plant Disease
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• v.16 no.2
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• pp.176-182
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• 2010

Occurrence of plant diseases is dependent on various factors in the agricultural system. Due to recent extensive environmental climate changes, i.e. global warming, agricultural systems such as planting dates and cultivars are being affected. Gradual transition in disease occurrence and incidence in the agricultural fields can also be affected by direct and/or indirect environmental changes. In this study, we evaluated disease occurrence and incidence in soybean plants to investigate whether it could be related with cultivars, planting dates and geographical differences in Korea in 2008. Soybean cultivars including 'Taekwang', 'Pungsan', 'Cheongja 3', 'Saeol', and 'Dawon' were planted in four different dates, May 15, June 1, June 15, and June 30, in two locations, Suwon, and Naju. Soybean diseases such as wild fire and bacterial pustule were mainly found depending on cultivars, planting dates, and areas. Wild fire occurred severely on cv. 'Taekwang' while bacterial blight did on cv. 'Dawon' among tested cultivars. Disease developments of wild fire and bacterial blight generally decreased in delayed planting regardless of cultivars.

• Korean Journal of Agricultural and Forest Meteorology
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• v.23 no.1
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• pp.15-33
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• 2021

In this study, the possibility of discriminating Fire blight (FB) infection tested using the hyperspectral imagery. The reflectance of healthy and infected leaves and branches was acquired with 5 nm of full width at high maximum (FWHM) and then it was standardized to 10 nm, 25 nm, 50 nm, and 80 nm of FWHM. The standardized samples were divided into training and test sets at ratios of 7:3, 5:5 and 3:7 to find the optimal bands of FWHM by the decision tree analysis. Classification accuracy was evaluated using overall accuracy (OA) and kappa coefficient (KC). The hyperspectral reflectance of infected leaves and branches was significantly lower than those of healthy green, red-edge (RE) and near infrared (NIR) regions. The bands selected for the first node were generally 750 and 800 nm; these were used to identify the infection of leaves and branches, respectively. The accuracy of the classifier was higher in the 7:3 ratio. Four bands with 50 nm of FWHM (450, 650, 750, and 950 nm) might be reasonable because the difference in the recalculated accuracy between 8 bands with 10 nm of FWHM (440, 580, 640, 660, 680, 710, 730, and 740 nm) and 4 bands was only 1.8% for OA and 4.1% for KC, respectively. Finally, adding two bands (550 nm and 800 nm with 25 nm of FWHM) in four bands with 50 nm of FWHM have been proposed to improve the usability of multispectral image sensors with performing various roles in agriculture as well as detecting FB with other combinations of spectral bands.

• Journal of Forest and Environmental Science
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• v.28 no.1
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• pp.24-29
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• 2012

This paper assesses the stmpage value of Korean white pine (Pinus koraiensis) stands in the Research Forest of Kangwon National University. Assessment was done by means of the cost value method (Faustmann formula) for age class I, Glaser method for age class II-V, and inversion market method for age class over VI. Generally the value of stumpage is calculated by the inversion market method in the market. However, immature trees and middle age class trees are not assessed in market, and the Korean forest is not old enough to harvest. So, when forests are damaged by attacks from forest fire, blight and harmful insects, the forest cannot be compensated for the loss from the government or insurance company. For this reason, the value of all-age class trees are calculated by using appropriate methods. As a result, the value of age I class stands (0.3 ha) is calculated as 1,786,305 (won), age II-Vclass stands (22.1 ha) 206,677,975 (won) and age VI class and over stands (24.8 ha) 523,789,603 (won).

• The Plant Pathology Journal
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• v.38 no.4
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• pp.410-416
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• 2022

Erwinia amylovora, the causal agent of fire-blight disease in apple and pear trees, was first isolated in South Korea in 2015. Although numerous studies, including omics analyses, have been conducted on other strains of E. amylovora, studies on South Korean isolates remain limited. In this study, we conducted a comparative proteomic analysis of the strain TS3128, cultured in three media representing different growth conditions. Proteins related to virulence, type III secretion system, and amylovoran production, were more abundant under minimal conditions than in rich conditions. Additionally, various proteins associated with energy production, carbohydrate metabolism, cell wall/membrane/envelope biogenesis, and ion uptake were identified under minimal conditions. The strain TS3128 expresses these proteins to survive in harsh environments. These findings contribute to understanding the cellular mechanisms driving its adaptations to different environmental conditions and provide proteome profiles as reference for future studies on the virulence and adaptation mechanisms of South Korean strains.

• Journal of Microbiology and Biotechnology
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• v.33 no.9
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• pp.1141-1148
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• 2023

Herein, we explored the potential of the apple's core microbiota for biological control of Erwinia amylovora, which causes fire blight disease, and analyzed the structure of the apple's bacterial community across different tissues and seasons. Network analysis results showed distinct differences in bacterial community composition between the endosphere and rhizosphere of healthy apples, and eight taxa were identified as negatively correlated with E. amylovora, indicating their potential key role in a new control strategy against the pathogen. This study highlights the critical role of the apple's bacterial community in disease control and provides a new direction for future research in apple production. In addition, the findings suggest that using the composition of the apple's core taxa as a biological control strategy could be an effective alternative to traditional chemical control methods, which have been proven futile and environmentally harmful.

• The Plant Pathology Journal
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• v.39 no.4
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• pp.397-408
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• 2023

Fire blight disease, caused by Erwinia amylovora, is a devastating affliction in apple cultivation worldwide. Chemical pesticides have exhibited limited effectiveness in controlling the disease, and biological control options for treating fruit trees are limited. Therefore, a relatively large-scale survey is necessary to develop microbial agents for apple trees. Here we collected healthy apple trees from across the country to identify common and core bacterial taxa. We analyzed the endophytic bacterial communities in leaves and twigs and discovered that the twig bacterial communities were more conserved than those in the leaves, regardless of the origin of the sample. This finding indicates that specific endophytic taxa are consistently present in healthy apple trees and may be involved in vital functions such as disease prevention and growth. Furthermore, we compared the community metabolite pathway expression rates of these endophyte communities with those of E. amylovora infected apple trees and discovered that the endophyte communities in healthy apple trees not only had similar community structures but also similar metabolite pathway expression rates. Additionally, Pseudomonas and Methylobacterium-Methylorobrum were the dominant taxa in all healthy apple trees. Our findings provide valuable insights into the potential roles of endophytes in healthy apple trees and inform the development of strategies for enhancing apple growth and resilience. Moreover, the similarity in cluster structure and pathway analysis between healthy orchards was mutually reinforcing, demonstrating the power of microbiome analysis as a tool for identifying factors that contribute to plant health.

• Korean journal of applied entomology
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• v.16 no.1 s.30
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• pp.47-53
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• 1977

Bacterial diseases of soybean has been recognized as a limiting factor of soybean production in Korea as it was estimated to cause around 10 percent of yield losses annually. The purpose of the study is to obtain information on the diseases through proving the kinds of pathogens and epidemiology, The wire brush method and multineedle appeared to be the best way of inoculation under all circumstances. Wire brush method, especially, was effective in shortening the incubation period and manifesting the lesion development by introducing more inoculum per unit of area. In case of spray inoculation it was necessary to apply a small amount(1 : 1,000) of wetting agent, twin-20, otherwise it was unabled to produce the diseases under field conditions. Two kinds of bacterial diseases caused by Pseudomonas glycinea and Xanthomonas phaseoli var. sljense were found from surveyed areas in Kore. Wild fire disease on soybean caused by Pseudomonas tabaci had not detectable during the experiment although there were several reports on the disease from other countries. when the pathogens were introduced into sterile soil, bacterial leaf blight pathogen could exsisted until 30 days while bacterial pustule pathogen survived only 4 days under the natural conditions of later June. Both bacteria, however, could produce the disease after more than 10 months period of storage in refrigerator when they were exsisted in infected plant tissues. In warehouse, non-temperature controlled, the bacteria lose their infectability within 6 months period from October to April even though they exsisted in infected tissues. Surface infested seeds with the pathogens could not produced the diseases on seedling stages of soybean plants when the seeds were planted in sterile soil after inoculation by dipping the seeds into bacterial suspensions, although germination was depressed by the pathogens when the seeds were planted on agar media.