• Research in Plant Disease
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• v.15 no.3
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• pp.222-229
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• 2009

A Pseudomonas strain SG3 producing biosurfactant and showing antifungal and insecticidal activities was isolated from agricultural soil severely contaminated with machine oils. The antagonistic bacterium inhibited mycelial growth of all of the tested fungal pathogens. The fermentation broth of SG3 also effectively suppressed the development of various plant diseases including rice blast, tomato gray mold, tomato late blight, wheat leaf rust, barley powdery mildew and red pepper anthracnose. An antifungal substance was isolated from the fermentation broth of SG3 by ethyl acetate partitioning, silica gel column chromatography and preparative HPLC under the guide of bioassay. The chemical structure of the antifungal substance was determined to be rhamnolipid B by mass and NMR spectral analyses. The antifungal biosurfactant showed a potent in vivo antifungal activity against gray mold and late blight on tomato plants. In addition, rhamnolipid B inhibited mycelial growth of B. cinerea causing tomato gray mold and zoospore germination and mycelial growth of P. infestans causing tomato late blight. Pseudomonas sp. SG3 producing rhamnolipid B could be used as a new biocontrol agent for the control of plant diseases occurring on tomato plants.

• Research in Plant Disease
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• v.17 no.1
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• pp.1-12
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• 2011

Incidence of Phytophthora blight of hot pepper (Capsicum annuum) and yield (fresh weight) of pepper fruits were investigated at four separate fields located in Cheongwon, Boeun, Eumsung, and Goesan, which are major pepper production areas in Chungcheongbuk-Do. In all of the experimental fields except the Goesan field, increased incidence of Phytophthora blight led to decreased yield of pepper fruits. The harvest time in which the yield of red pepper fruits was highly correlated with the incidence of Phytophthora blight was different between areas: it was highly correlated in the third harvest in Cheongwon (y=-11.0x+435.2, $r^2$=0.99), but in the second harvest in Boeun (y=-15.0x+944.6, $r^2$=0.76). In contrast, there was a very low correlation between the pepper yield and the disease incidence in Goesan in which pepper seedlings grafted on resistant stocks were planted. The final disease incidence in the Cheongwon experimental field reached 100% more than 40 days later in 2007 compared with that in 2006. The control threshold of Phytophthora blight in the pepper fields where disease incidence had been lower than 5% was set as 0.8% disease incidence, which caused less than 5% yield loss.

• Research in Plant Disease
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• v.11 no.2
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• pp.146-151
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• 2005

A new bacterial disease of sesame(Sesamum indicum) was observed on field-grown plants in Suwon, Hongchun and Yeonchun in 2000. Leaf symptoms initially appeared as water-soaked spots that gradually enlarged, became necrotic and were often bordered by a small zone of lemon yellow tissue. In the case of severe infection, dead leaves were defoliated. Isolations made from diseased leaves on yeast extract dextrose calcium carbonate agar yielded nearly pure cultures of a yellow-pigmented bacterium typical of a xanthomonad. Two bacterial strains were purified and used for farther tests. Pathogenicity of strains was confirmed on 3-week-old sesame plants sprayed with bacterial suspensions containing $10^{8}cfu/ml$ of phosphate buffered saline. The Biolog and fatty acid analyses of the two strains(SL3451 and SL3476) 1mm sesame leaf blight showed that they could be identified as ft campestris pv. sesami because of their high similarity to the tester strain(X. campestris pv. sesami LMG865) with a match probability of $100\%$. The bacterium grew well between 18 and 36$^{\circ}C$, but optimum temperature was $27^{\circ}C$ on LB broth. This is the first report of bacterial blight of sesame in Korea. Symptoms of bacterial blight of sesame are difficult to differentiated with those of bacterial leaf spot caused by Pseudomonas syringae pv. sesami.

• Weed & Turfgrass Science
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• v.5 no.2
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• pp.101-104
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• 2016

Curvularia leaf blight of creeping bentgrass (Agrostis stolonifera) putting green by caused Curvularia trifolii was observed in Hapcheon, Korea. In July to September 2014, curvularia leaf blight developed on leaf blades of creeping bentgrass as small water-soaked lesions that subsequently turned into dark-colored, necrotic spots. The spots were expanded and became gray, grayish-brown, or light brown, circular to oblong lesions with purple to dark brown borders that often were surrounded by a yellow halo. The necrotic lesions coalesced, became irregular in shape and caused tip or complete blighting of the leaves. Blighted leaf blades appeared grayish-white to tan. The fungus was identified by morphological characters and 16S rDNA sequencing as C. trifolii. Conidia of the pathogen were short, with predominantly 3-septa, straight or often curved, with end cells frequently paler than intermediate cells. Size of the 3-septate conidia in culture are $26{\sim}28{\times}11{\sim}12{\mu}m$. Pathogenicity of the fungus was proved by artificial inoculation on the host. This is the first report of C. trifolii causing leaf blight on creeping bentgrass in Korea.

• Research in Plant Disease
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• v.18 no.1
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• pp.24-28
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• 2012

The rice diseases occurring on the transgenic rice plant carrying protox gene (CPPO06) was assessed and compared with other varieties of rice such as Dongjin, Chucheong, Ilpeum, and Onnuri in the fields located in Cheongwon of Chungbuk, Suwon of Gyeunggi, and Gwangju of Chonnam. In the field of Cheongwon, the diseases such as blast, leaf spot, sheath blight and Fusarium blight were observed. False smut were observed only in the field of Suwon, where the ratio of diseased plants was 0.28% in CPPO06 and 0.37% in Onnuri, respectively. In the field of Gwangju, leaf spot caused by Cochlioborus miyabeanus was the most severely occurring disease among rice diseases mentioned above. Fusarium blight occurred in all the 3 fields, which were more severe in CPPO06 plants treated with or without oxadiazon as the herbicide. Except for Fusarium blight, there was no significant difference in the rice diseases as blast, leaf spot, sheath blight and false smut between CPPO06 and other rice varieties.

• Research in Plant Disease
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• v.26 no.4
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• pp.250-255
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• 2020

In order to find if a ferulic acid (FA) can be used as a selection index in cereal breeding for resistance to head blight and mycotoxin production, we analyzed FA in the grains of 80 cultivars of barley, rice, and wheat. FA content ranged 1.66-2.77 mg/g in barley (n=20), 0.56-1.53 mg/g in wheat (n=40), and 0.91-2.13 mg/g in rice (n=20). Among these, 7 cultivars each of barley and wheat with different FA content were tested for head blight and mycotoxin production by 2 Fusarium graminearum and 2 F. asiaticum strains. Mean pathogenicity of the wheat cultivars was significantly less than that of barley with higher FA and among wheat cultivars, there was no correlation between FA content and pathogenicity. Mycotoxin production was also lower in the wheat than in the barley as pathogenicity. However, pathogenicity and toxins produced by F. asiaticum were negatively correlated with FA content in barley. These results indicate that FA is not a resistance factor to head blight by F. asiaticum and F. graminearum or its mycotoxin production in barley and wheat.

• Korean Journal of Environmental Biology
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• v.38 no.4
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• pp.724-732
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• 2020

Phytophthora capsici is the organism that causes Phytophthora blight which infects red pepper plants prolifically, ultimately leading to crop loss. A previous study revealed that Enterobacter asburiae ObRS-5 suppresses Phytophthora blight in both red pepper and Ligularia fischeri plants. In order to determine whether the induced systemic resistance (ISR) was triggered by pre-infection with the ObRS-5 strain, we conducted quantitative PCR using primers for PR1, PR4, and PR10, which correlate with systemic resistance in red-pepper plants. In our results, red pepper plants treated with the ObRS-5 strain demonstrated increased expression of all three systemic resistance genes when compared to controls in the glasshouse seedling assay. In addition, treatment of red peppers with the ObRS-5 strain led to reduced Phytophthora blight symptoms caused by P. capsici, whereas all control seedlings were severely affected. Perhaps most importantly, E. asburiae ObRS-5 was shown to induce the ISR response in red peppers without inhibiting growth. These results support that the defense mechanisms are triggered by ObRS-5 strain prior to infection by P. capsici and ObRS-5 strain-mediated ISR action are linked events for protection to Phytophthora blight.

• 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.

• Korean Journal of Plant Resources
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• v.36 no.1
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• pp.100-106
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• 2023

In order to control the fire blight disease, all plants within the radius of the diseased orchard were removed in the early stage of the outbreak, or antibiotics control was performed for prevention. Since the beginning of antibiotics use on plants, the potential for development of resistance to antibiotics by the plant pathogen and unintended detrimental effects on the fruit trees and environment has become a problem. The purpose of this study is to determine the degree of phytotoxicity to fruit trees caused by excessive spraying of the fire blight disease disinfectant and to establish basic data for safe disinfectant guide. We analyzed whether damage to the fruit tree and the maximum residual limit of fruit was exceeded when three kinds of the fire blight disease disinfectants were continuously sprayed in excess of the number of safe use during the growing season. There was no phytotoxicity in apple 'Fuji' and pear 'Niitaka', and oxolinic acid was detected beyond the limit of quantitation in 'Fuji' grown without a bag, and the other disinfectants were detected below the maximum residue limit. When these disinfectants are continuously sprayed in excess of the number of safe, phytotoxicity may remain on the fruit. Therefore, it is necessary to observe the prescribed dilution factor and observe the safe frequency and the timing of use.

• The Korean Journal of Mycology
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• v.50 no.4
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• pp.331-341
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• 2022

This study was conducted to identify yeast species isolated from domestic pear blossom through gene sequencing and analysis of morphological characteristics, and to confirm specific yeast species inhibitory effects toward fire blight in immature apples, pears, and crab apple blossoms. Yeast morphological characteristics were consistent with the known characteristics of Aureobasidium pullulans. Nucleotide sequencing of the D1/D2 region of large-subunit (LSU) 26S ribosomal DNA and the internal transcribed spacer (ITS) region confirmed its identity as A. pullulans (MHAU2101). Inoculation of immature fruits with A. pullulans MHAU2101 before exposure to Erwinia amylovora prevented fire blight symptoms in apples and pears. A. pullulans MHAU2101 treated crab apple blossoms had a significantly lower flower infection rate than untreated blossoms, revealing 64% of the potency of streptomycin. The A. pullulans MHAU2101 treated group also displayed lower E. amylovora density in both pistil and hypanthium compared to the untreated group, especially in the hypanthium. This study confirms that A. pullulans MHAU2101 isolated from domestic pear blossom can effectively suppress the onset of fire blight.