• Research in Plant Disease
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• v.20 no.2
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• pp.101-106
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• 2014

Citrus canker caused by Xanthomonas citri subsp. citri (Xcc) is one of the most important diseases on citrus. Although Satsuma mandarin cultivating mostly in Korea is moderately resistance to canker, occurrence of the disease were more frequently reported since last decade. Like other diseases in citrus, citrus canker was mainly protected by chemical fungicide in the field. Due to the side effect of the chemicals, alternative method of disease control is recently required. In this study four rhizobacterial strains TRH423-3, MRL408-3, THJ609-3 and TRH415-2 are selected by testing its antifungal activity against Xcc. Pre-inoculation with the selected rhizobacterial strains caused disease suppression on the citrus leaves after inoculation with the citrus canker pathogen. Similarly, in the field test symptoms of citrus canker were less developed in the citrus trees applied several times with the selected rhizobacterial strains compared with those of untreated trees. Therefore, it is suggested that the selected rhizobacterial strains may be valuable as an alternative method in the environment-friendly citrus farm.

• The Plant Pathology Journal
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• v.15 no.3
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• pp.137-143
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• 1999

A novel chromosomal gene tagging technique using a specific fragment of the fatty acid desaturase-like open reading frame (des-like ORF) from the tox-argK gene cluster of Pseudomonas syringae pv. phaseolicola was developed to identify Xanthomonas spp.released into the environment as biocontrol agents. X. campestris pv. convolvuli FB-635, a pathogen of Convolvulus arvensis L., (bindweed), was chosen as the organism in which to develop and test the system. A 0.52 kb DES fragment amplified from P. syringae pv. phaseolicola C-199 was inserted into pGX15, a cosmid clone containing a 10.3 kb Eco RI-HindIII fragment derived from the xanthomonadin biosynthetic gene cluster contained in plasmid pIG102, to create a pigG::DES insertion. The 10.8 kb EcoRI-BamHI fragment carrying the pigG:: DES insertion was cloned into pLAFR3 to generate pLXP22. pLXP22 was then conjugated into X. campestris pv. convolvuli FB-635 and the pigG::DES insertion integrated into the bacterial chromosome by marker exchange. Rifampicin resistant, tetracycline sensitive, starch hydrolyzing, white colonies were used to differentiate the marked strain from yellow pigmented wild-type ones. PCR primers specific for the unique DES fragment were used for direct detection of the marked strain. Result showed the marked strain could be detected at very low levels even in the presence of high levels of other closely related or competitive bacteria. This PCR-based DES-tagging system provides a rapid and specific tool for directly monitoring the dispersal and persistence of Xanthomonas spp.released into the environment.

• Research in Plant Disease
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• v.14 no.3
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• pp.165-170
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• 2008

One hundred and three isolates of Xanthomonas oryzae pv. oryzae in Korea were evaluated for their virulence on four near-isogenic lines (NILs) containing a single resistance gene, and Korean differential varieties. The resistant gene backgrounds of Cheongcheongbyeo, Pungsanbyeo, Hangangchalbyeo, Milyang42 were not completely understood and they were not suited for the classification of X. oryzae pv. oryzae. Four NILs, IRBB101, IRBB103, IRBB105, and IRBB107 were difference for characterizing races of X. oryzae pv. oryzae because they have a single resistance gene. These NILs may be useful differential set in examining pathogenic races of X. oryzae pv. oryzae in Korea. Based on the virulence of 103 isolates to new differential varieties, they were classified into 3 races.

• The Plant Pathology Journal
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• v.31 no.4
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• pp.343-349
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• 2015

Citrus canker caused by Xanthomonas citri subsp. citri (Xcc) is one of the most important bacterial diseases of citrus. Because citrus canker is not found in many countries including European Union and Australia, Xcc is strictly regulated in order to prevent its spread. In this study, the effects of X-irradiation on Xcc growth either in the suspension or on the surface of citrus fruits were investigated. The suspension containing $1{\times}10^7cfu/ml$ of Xcc was irradiated with different absorbed doses of X-irradiation ranging from 50 to 400 Gy. The results showed that Xcc was fully dead at 400 Gy of X-irradiation. To determine the effect of X-irradiation on quarantine, the Xcc-inoculated citrus fruits were irradiated with different X-ray doses at which Xcc was completely inhibited by an irradiation dose of 250 Gy. The $D_{10}$ value for Xcc on citrus fruits was found to be 97 Gy, indicating the possibility of direct application on citrus quarantine without any side sterilizer. Beside, presence of Xcc on the surface of asymptomatic citrus fruits obtained from citrus canker-infected orchards was noted. It indicated that the exporting citrus fruits need any treatment so that Xcc on the citrus fruits should be completely eliminated. Based on these results, ionizing radiation can be considered as an alternative method of eradicating Xcc for export of citrus fruits.

• Korean Journal of Organic Agriculture
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• v.7 no.1
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• pp.137-146
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• 1998

Various rhizobacteria was isolated, and was bacterialized into the substrates to clarify the plant growth promoting effects of rhizobacteria on the early growth of red peper seedlings. Total 125 bacterial isolates were primarily isolated and purified from the soils in greenhouse. And four strains were finally screened, based on the antifungal activities against Fusarium sp., Pythium sp. and Rhizoctonia sp. of red pepper plants. The strongest antifungal strain RB 109 has a antagonistic activity against Fusarium sp., Pythium sp. and Rhizoctonia sp. in terms of 66.0%, 65.0% and 66.1%. Early growth of red pepper seedlings was promoted, when cultured solution of rhizobacteria RB 109 was bacterialized into the substrates. Antifungal rhizobacteria RB 109 was identified as Pseudomonas sp. related strains, which has a similarity of 82% to the Pseudomonas sp.

• The Plant Pathology Journal
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• v.34 no.6
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• pp.490-498
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• 2018

Panicle blight and seed rot disease caused mainly by Burkholderia glumae and Burkholderia gladioli is threatening rice cultivation worldwide. The bacteria have been reported as seed-borne pathogens from rice. Accurate detection of both pathogens on the seeds is very important for limiting the disease dissemination. Novel primer pairs targeting specific molecular markers were developed for the robust detection of B. glumae and B. gladioli. The designed primers were specific in detecting the target species with no apparent cross-reactions with other related Burkholderia species at the expected product size. Both primer pairs displayed a high degree of sensitivity for detection of B. glumae and B. gladioli separately in monoplex PCR or simultaneously in duplex PCR from both extracted gDNA and directly preheated bacterial cell suspensions. Limit of detection was as low as 0.1 ng of gDNA of both species and $3.86{\times}10^2cells$ for B. glumae and $5.85{\times}10^2cells$ for B. gladioli. On inoculated rice seeds, the designed primers could separately or simultaneously detect B. glumae and B. gladioli with a detection limit as low as $1.86{\times}10^3cells$ per rice seed for B. glumae and $1.04{\times}10^4cells$ per rice seed of B. gladioli. The novel primers maybe valuable as a more sensitive, specific, and robust tool for the efficient simultaneous detection of B. glumae and B. gladioli on rice seeds, which is important in combating rice panicle blight and seed rot by early detection and confirmation of the dissemination of pathogen-free rice seeds.

• Korean Journal of Environmental Biology
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• v.40 no.4
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• pp.398-404
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• 2022

Bis(2-ethylhexyl) phthalate (DEHP) is one of the plasticizers used in the polyvinyl chloride(PVC) industry. It is known to be easily released into the environment. In this study, we investigated effects of DEHP on growth, metabolic pathway, and virulence gene expression in soil-borne bacterial plant pathogen, Pectobacterium carotovorum SCC1 using in vitro assays. As a result, DEHP at 20 ㎍ mL^-1 did not affect the growth, cell membrane permeability, or ATPase activity of P. carotovorum SCC1. However, it decreased succinyl-CoA synthase (SCS) activity in the tricarboxylic acid (TCA) cycle. Relative expression levels of virulence genes encoding pectate lyase and pectin were differentially influenced by DEHP treatment. These results suggest that biological characteristics of P. carotovorum might be influenced by DEHP in soil.

• The Plant Pathology Journal
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• v.39 no.1
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• pp.52-61
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• 2023

Fire blight, caused by Erwinia amylovora, is one of the major bacterial disease of apple and pear, causing enormous economic losses worldwide. Several control measures against E. amylovora have been reported till date, however, none of them have proved to be effective significantly against the pathogen. In this study, mechanisms of the copper-based control agents (CBCAs): copper oxychloride (COCHL), copper oxide (COX), copper hydroxide (CHY), copper sulfate basic (CSB), and tribasic copper sulfate (TCS) and their disease severity reduction efficacy against E. amylovora were analyzed. Bis-1,3-dibutylbarbituric acid trimethine oxonol, carboxyl fluorescein diacetate succinimidyl ester, and 5-cyano-2,3-ditolyl tetrazolium chloride staining were used to check the damage of membrane potential, cytoplasmic pH_in, and respiration of CBCAs-treated E. amylovora, respectively. High disturbance in the membrane potential of E. amylovora was found under COX and COCHL treatments. Similarly, higher significant changes in the inner cytoplasmic pH_in were observed under COX, COCHL, and TCS treatment. CHY and COCHL-treated E. amylovora showed a significant reduction in respiration. In vitro bioassay results revealed that CHY, CSB, and TCS at 2,000 ppm reduced the severity of fire blight both in pre- and post-treatment of CBCAs in immature apple fruits and seedlings. Overall, the most effective CBCAs against E. amylovora could be CHY at 2,000 ppm as its showed inhibition mechanisms and disease severity reduction.

• Research in Plant Disease
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• v.13 no.2
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• pp.110-114
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• 2007

Anthracnose fungus was most pathogenic on soybean sprout, of the fungi and bacteria isolated from rotten sprout on market. Bacterial strains associated were not virulent. Dry heat (DHT) applied even as high as $65^{\circ}C$ for 30min. was not effective enough to eliminate the artificially inoculated Colletotrichum gloeosporioides propagules from seedllots. Hot water immersion treatment (HWT), at elevated temperature of $55^{\circ}C$ for 20 min, did eliminate the pathogen but reduced seed germinating and retarded sprout growth: Seed germination was practically acceptable when the seedlots were exposed to at $55^{\circ}C$ for 5 min, but about 20% anthracnose propagules survived. Accordingly, we have optimized the HWT scheme for 5 min at $60^{\circ}C$. This scheme was validated, at small to large scale production system, that surely rule out the possible carry over of the bacterial contaminant from seedlots. This result should improve the shelf-life of soybean sprout on the market.

• Research in Plant Disease
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• v.21 no.3
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• pp.208-214
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• 2015

To develop an effective biopesticide to control pepper anthracnose disease, an isolate which showed strong inhibitory effect on the mycelial growth and conidial germination of Colletotrichum acutatum was selected among the antagonistic bacterial isolates collected from pepper grown soil. The bacterial isolate was identified as Bacillus sp. KBC1004 using 16S rRNA sequence analysis. The liquid culture of KBC1004 was freeze-dried and formulated as a wettable powder(WP). The wettable powder form of KBC1004 required at least 24 hours to activate and to inhibit the conidial germination of C. acutatum. In vitro bioassay using the detached green pepper fruits, biocontrol activity of the WP was not recognizable in simultaneous inoculation, but significant disease suppression was observed pre-treatment (24 hr) of the WP before pathogen inoculation. In field experiment, 4 times foliar applications of the 1/500 diluted wettable powder from the end of June showed great control efficacy similar to that of the chemical fungicide application. These results suggest that the formulated WP product could be an alternative mean to control of pepper anthracnose disease in environmentally friendly farming practices.