• Mycobiology
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• v.36 no.4
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• pp.236-241
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• 2008

The colonization of an arbuscular mycorrhizal fungus Glomus intraradices BEG110 in the soil caused a decrease in disease severity in cucumber plants after fungal inoculation with Colletotrichum orbiculare. In order to illustrate the resistance mechanism mediated by G. intraradices BEG110, infection patterns caused by C. orbiculare in the leaves of cucumber plants and the host cellular responses were characterized. These properties were characterized using transmission electron microscopy on the leaves of cucumber plants grown in soil colonized with G. intraradices BEG110. In the untreated plants, inter- and intra-cellular fungal hyphae were observed throughout the leaf tissues during both the biotrophic and necrotrophic phases of infection. The cytoplasm of fungal hyphae appeared intact during the biotrophic phase, suggesting no defense response against the fungus. However, several typical resistance responses were observed in the plants when treated with G. intraradices BEG110 including the formation of sheaths around the intracellular hyphae or a thickening of host cell walls. These observations suggest that the resistance mediated by G. intraradices BEG110 most often occurs in the symplast of the host cells rather than in the apoplast. In addition, this resistance is similar to those mediated by biotic inducers such as plant growth promoting rhizobacteria.

• Proceedings of the Korean Society of Plant Pathology Conference
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• 2003.10a
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• pp.105.3-106
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• 2003

Bacillus subtilis strain BAC02-4 was tested for its ability induced systemic resistance(ISR) in rice against Magnaporthe grisea We extend these studies to investigate the biological induction of systemic resistance in rice following treatment with the inducer isolate BAC02-4 and naturally infested with Pyricularia oryzae. We also determine levels of ISR activity during the period between disease development and the onset of systemic resistance. Comparition of lesion number according to applied concentration of BAC02-4 to 'Nagdongbyeo' when naturally infested with the conidia of P. grisea. Results from the blast nusery trial using the 'Nagdongbyeo' showed very low rice blast severity with the inducer concentration of 10$\^$8/ cfu level. Considering the low level of treatment and untreated control were observed to have developed typical susceptible lesion type. Highest protection against the rice blast pathogen when applied three times with 5 days interval as root drench at 5 to 6 leaf stage before pathogen challenge. But higher dose of bacterial inducer produced a little stunted plants with less number lesions and delayed disease development. Diseased leaf area of treated with suspension of the isolate which gave about 80％ of control efficacy at 20 days later comparable to that in noninfested, inducer-free soil.

• Journal of Microbiology and Biotechnology
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• v.19 no.10
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• pp.1250-1258
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• 2009

Bacillus spp., as a type of plant growth-promoting rhizobacteria (PGPR), were studied with regards promoting plant growth and inducing plant systemic resistance. The results of greenhouse experiments with tobacco plants demonstrated that treatment with the Bacillus spp. significantly enhanced the plant height and fresh weight, while clearly lowering the disease severity rating of the tobacco mosaic virus (TMV) at 28 days post-inoculation (dpi). The TMV accumulation in the young non-inoculated leaves was remarkably lower for all the plants treated with the Bacillus spp. An RT-PCR analysis of the signaling regulatory genes Coil and NPR1, and defense genes PR-1a and PR-1b, in the tobacco treated with the Bacillus spp. revealed an association with enhancing the systemic resistance of tobacco to TMV. A further analysis of two expansin genes that regulate plant cell growth, NtEXP2 and NtEXP6, also verified a concomitant growth promotion in the roots and leaves of the tobacco responding to the Bacillus spp.

• Journal of Microbiology and Biotechnology
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• v.17 no.4
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• pp.586-593
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• 2007

Seed coating by a phenazine-producing bacterium, Pseudomonas chlororaphis O6, induced dose-dependent inhibition of germination in wheat and barley seeds, but did not inhibit germination of rice or cucumber seeds. In wheat seedlings grown from inoculated seeds, phenazine production levels near the seed were higher than in the roots. Deletion of the gacS gene reduced transcription from the genes required for phenazine synthesis, the regulatory phzI gene and the biosynthetic phzA gene. The inhibition of seed germination and the induction of systemic disease resistance against a bacterial soft-rot pathogen, Erwinia carotovora subsp. carotovora, were impaired in the gacS and phzA mutants of P chlororaphis O6. Culture filtrates of the gacS and phzA mutants of P. chlororaphis O6 did not inhibit seed germination of wheat, whereas that of the wild-type was inhibitory. Our results showed that the production of phenazines by P. chlororaphis O6 was correlated with reduced germination of barley and wheat seeds, and the level of systemic resistance in tobacco against E. carotovora.

• International Journal of Industrial Entomology and Biomaterials
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• v.35 no.2
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• pp.63-70
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• 2017

Native fluorescent pseudomonas bacteria were isolated from rhizosphere soil of mulberry and were evaluated against powdery mildew. In vitro conidial germination study showed significant (P<0.05) variation in conidial germination by bacterial strains Pf1 and Pf3. Mildew incidence was significantly varied due to treatment with various pseudomonas strains in vivo. Significantly (P<0.05) less mildew incidence was in plants treated with the bacterial strain Pf1 (9.11%) followed by Pf3 (13.48%) controlling 69.40% and 54.75% respectively compared with untreated control. Similarly, mildew severity was least (8.51%) in plants treated with strain Pf1 followed by Pf5 (9.23%) and Pf3 (9.72%) controlling the severity by 84.51%, 77.01% and 71.96% respectively compared with control. The bacterial strains significantly influenced biochemical constituents such as chlorophyll, protein and soluble sugar content of the mulberry leaf. Similarly, bacterial strains significantly increased the activity of the peroxidase (PO) and Polyphenol oxydase (PPO) activity from $7^{th}$ day up to the $28^{th}$ day after treatment. The strain Pf1, Pf3 and Pf5 exhibited a marked enhancement in the peroxidase at different periods of infection. Significant (P<0.01) negative correlation was found between powdery mildew severity with phenol content ($R^2=0.67$) as well as peroxidase ($R^2=0.92$) and polyphenol oxidase ($R^2=0.72$) activity thus confirms induction of systemic resistance in mulberry by pseudomonas bacteria. The study shows scope for exploration of rhizosphere fluorescent pseudomonas bacteria for induction of systemic resistance in mulberry to contain powdery mildew disease effectively.

• The Plant Pathology Journal
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• v.36 no.3
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• pp.255-266
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• 2020

Plant immune responses can be triggered by chemicals, microbes, pathogens, insects, or abiotic stresses. In particular, induced systemic resistance (ISR) refers to the activation of the immune system due to a plant's interaction with beneficial microorganisms. The phenolic compound, 2,4-diacetylphloroglucinol (DAPG), which is produced by beneficial Pseudomonas spp., acts as an ISR elicitor, yet DAPG's mechanism in ISR remains unclear. In this study, transgenic Arabidopsis thaliana plants overexpressing the DAPG hydrolase gene (phlG) were generated to investigate the functioning of DAPG in ISR. DAPG was applied onto 3-week-old A. thaliana Col-0 and these primed plants showed resistance to the pathogens Botrytis cinerea and Pseudomonas syringae pv. tomato DC3000. However, in the phlG transgenic A. thaliana, the ISR was not triggered against these pathogens. The DAPG-mediated ISR phenotype was impaired in transgenic A. thaliana plants overexpressing phlG, thus showing similar disease severity when compared to untreated control plants. Furthermore, the DAPG-treated A. thaliana Col-0 showed an increase in their gene expression levels of PDF1.2 and WRKY70 but this failed to occur in the phlG transgenic lines. Collectively, these experimental results indicate that jasmonic acid/ethylene signal-based defense system is effectively disabled in phlG transgenic A. thaliana lines.

• The Plant Pathology Journal
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• v.29 no.2
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• pp.209-220
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• 2013

Root colonization by Pseudomonas chlororaphis O6 induces systemic drought tolerance in Arabidopsis thaliana. Microarray analysis was performed using the 22,800-gene Affymetrix GeneChips to identify differentially-expressed genes from plants colonized with or without P. chlororaphis O6 under drought stressed conditions or normal growth conditions. Root colonization in plants grown under regular irrigation condition increased transcript accumulation from genes associated with defense, response to reactive oxygen species, and auxin- and jasmonic acid-responsive genes, but decreased transcription factors associated with ethylene and abscisic acid signaling. The cluster of genes involved in plant disease resistance were up-regulated, but the set of drought signaling response genes were down-regulated in the P. chlororaphis O6-colonized under drought stress plants compared to those of the drought stressed plants without bacterial treatment. Transcripts of the jasmonic acid-marker genes, VSP1 and pdf-1.2, the salicylic acid regulated gene, PR-1, and the ethylene-response gene, HEL, also were up-regulated in plants colonized by P. chlororaphis O6, but differed in their responsiveness to drought stress. These data show how gene expression in plants lacking adequate water can be remarkably influenced by microbial colonization leading to plant protection, and the activation of the plant defense signal pathway induced by root colonization of P. chlororaphis O6 might be a key element for induced systemic tolerance by microbes.

• The Plant Pathology Journal
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• v.29 no.2
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• pp.136-143
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• 2013

Microbial communities that are associated with plant roots are highly diverse and harbor tens of thousands of species. This so-called microbiome controls plant health through several mechanisms including the suppression of infectious diseases, which is especially prominent in disease suppressive soils. The mechanisms implicated in disease suppression include competition for nutrients, antibiosis, and induced systemic resistance (ISR). For many biological control agents ISR has been recognized as the mechanism that at least partly explains disease suppression. Implications of ISR on recruitment and functioning of the rhizosphere microbiome are discussed.

• Microbiology and Biotechnology Letters
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• v.35 no.1
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• pp.41-44
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• 2007

This study was carried out to investigate the effects of wood vinegar on growth and resistance of peppers. It was observed that heights and dried weights of the peppers treated with diluted wood vinegar were increased, especially 1:500 diluted wood vinegar was the most effective. The Wood vinegar also showed antibacterial activity against Xanthomonas axonopodis pv. vesicatoria directly. The growth of X. axonopodis pv. vesicatoria was completely inhibited when incubated for 12 hours at $30^{\circ}C$ with non diluted wood vinegar. The peppers applied wood vinegar did not show induced systemic resistance after injecting X. axonopodis pv. vesicatoria.

• The Plant Pathology Journal
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• v.17 no.6
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• pp.370.5-371
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• 2001