• The Plant Pathology Journal
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• v.37 no.1
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• pp.57-71
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• 2021

Rice sheath blight (ShB), caused by Rhizoctonia solani Kühn AG1-IA, is one of the destructive rice diseases worldwide. The aims of this study were to develop biocontrol strategies focusing on field sanitation and foliar application with a biocontrol agent for ShB management. Streptomyces padanus PMS-702 showed a great antagonistic activity against R. solani. Fungichromin produced by S. padanus PMS-702, at 3.07 mg/l inhibited 50% mycelial growth, caused leakage of cytoplasm, and inhibited the formation of infection structures of R. solani. Fungichromin could reach to 802 mg/l when S. padanus PMS-702 was cultured in MACC broth for 6 days. Addition of 0.5% S. padanus PMS-702 broth into soil decreased the survival rate of the pathogen compared to the control. Soil amended with 0.5% S. padanus broth and 0.5% tea seed pomace resulted in the death of R. solani mycelia in the infested rice straws, and the germination of sclerotia was inhibited 21 days after treatment. Greenhouse trials revealed that S. padanus cultured in soybean meal-glucose (SMGC-2) medium after mixing with different surfactants could enhance its efficacy for inhibiting the pathogen. Of six surfactants tested, the addition of 2% tea saponin was the most effective in suppressing the pathogen. S. padanus broth after being fermented in SMGC-2, mixed with 2% tea saponin, diluted 100 fold, and sprayed onto rice plants significantly reduced ShB disease severity. Thus, S. padanus PMS-702 is an effective biocontrol agent. The efficacy of S. padanus PMS-702 for disease control could be improved through formulation.

• The Plant Pathology Journal
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• v.37 no.6
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• pp.580-595
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• 2021

Although late blight is an important disease in ecofriendly potato cultivation in Korea, it is highly dependent on the use of eco-friendly agricultural materials and the development of biological control technology is low. It is a necessary to develop an effective biocontrol agent to inactivate late blight in the field. AFB2-2 strain is a gram-positive with peritrichous flagella. It can utilize 20 types of carbon sources, like L-arabinose, and D-trehalose at 35℃. The optimal growth temperature of the strain is 37℃. It can survive at 20-50℃ in tryptic soy broth. The maximum salt concentration tolerated by AFB2-2 strain is 7.5% NaCl. AFB2-2 strain inhibited the mycelial growth of seven plant pathogens by an average inhibitory zone of 10.2 mm or more. Among the concentrations of AFB2-2, 10⁷ cfu/ml showed the highest control value of 85.7% in the greenhouse. Among the three concentrations of AFB2-2, the disease incidence and severity of potato late blight at 10⁷ cfu/ml was lowest at 0.07 and 6.7, respectively. The nucleotide sequences of AFB2-2 strain were searched in the NCBI GenBank; Bacillus siamensis strain KCTC 13613, Bacillus velezensis strain CR-502, and Bacillus amyloliquefaciens strain DSM7 were found to have a genetic similarity of 99.7%, 99.7%, and 99.5%, respectively. The AFB2-2 strain was found to harbor the biosynthetic genes for bacillomycin D, iturin, and surfactin. Obtained data recommended that the B. velezensis AFB2-2 strain could be considered as a promising biocontrol agent for P. infestans in the field.

• Journal of Microbiology and Biotechnology
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• v.4 no.2
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• pp.134-140
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• 1994

An antagonistic bacterium Pseudomonas stutzeri YPL-1 liberated extracellular chitinase and $\beta$-1,3-glucanase which are key enzymes in the decomposition of fungal hyphal walls. The lytic enzymes caused abnormal swelling and retreating at the hyphal tips of plant pathogenic fungus Fusarium solani in a dual culture. Scanning electron microscopy revealed the hyphal degradation of F. solani in the regions interacting with P. stutzeri YPL-1. The production of chitinase and properties of a crude preparation of the enzyme from P. stutzeri YPL-1 were investigated. Peak of the chitinase activity was detected after 4 hr of cultivation. The enzyme had optimum temperature and pH of 50$^{\circ}C$ and pH 5.3, respectively. The enzyme was stable in the pH range of 3.5 to 6.0 up to 50$^{\circ}C$. The enzyme was significantly inhibited by metal compounds such as $HgCl_2$, but was stimulated by $CoCl_2$. P. stutzeri YPL-1 produced high levels of the enzyme after 84 hr of incubation. Among the tested carbon sources, chitin was the most effective for the enzyme production, at the concentration level of 3%. As a source of nitrogen, peptone was the best for the enzyme production, at the concentration level of 4%. The maximum amount of enzyme was produced by cultivating the bacterium at a medium of initial pH 6.8.

• Journal of Microbiology and Biotechnology
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• v.26 no.3
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• pp.488-492
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• 2016

Rhodococcus species have become increasingly important owing to their ability to degrade a wide range of toxic chemicals and produce bioactive compounds. Here, we report isolation of the Rhodococcus sp. KB6, which is a new leaf-inhabiting endophytic bacterium that suppresses black rot disease in sweet potato leaves. We determined the 7.0 Mb draft genome sequence of KB6 and have predicted 19 biosynthetic gene clusters for secondary metabolites, including heterobactins, which are a new class of siderophores. Notably, we showed the first internal colonization of host plants with Rhodococcus sp. KB6 and discuss its potential as a biocontrol agent for sustainable agriculture.

• Microbiology and Biotechnology Letters
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• v.23 no.2
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• pp.236-242
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• 1995

Biological control of soilborne plant pathogens by the addition of antagonistic microorganisms to the soil may offer a practical supplement or alternative to existing disease management strategies that depend heavily on chemical pesticides. Soil amendment with antagonistic microbes was non-effective because of high cost, low efficacy, and inconvenient usage on the treatment course. Therefore, seed coating formulation for the application of biological seed treatments has been being to apply successful disease suppression for many important crops. The objectives of this study were to investigate the optimal condition for the spore production of biocontrol agent Bacillus subtilis YBL-7 and the liquid coating formulation that contained a suspension of a proper aqueous binder, as well as a ground fine solid particulate material. The maximum yield has been obtained from 60 hrs-old culture at 30$\circ$C in spore forming (SF) medium containing 0.8% nutrient broth, 0.05% yeast extract, 10$^{-1}$ M MgCl$^{2}$, 10$^{-4}$ M MnCl$^{2}$, 10$^{-5}$ M dipicolinic acid, and pH 6.5. The optimal condition of dried spore preparation was achieved when cells of B. subtilis YBL-7 was heat-dried with 50$\circ$C for 2 hrs.

• Journal of Microbiology and Biotechnology
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• v.24 no.10
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• pp.1327-1336
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• 2014

Bacillus amyloliquefaciens strain NJZJSB3 has shown antagonism of several phytopathogens in vitro, especially Sclerotinia sclerotiorum. Both the broth culture and cell suspension of strain NJZJSB3 could completely protect the detached leaves of canola (Brassica napus) from S. sclerotiorum infection. In pot experiments, the application of strain NJZJSB3 cell suspension ($10^8CFU/ml$) decreased the disease incidence by 83.3%, a result similar to commercially available fungicide (Dimetachlone). In order to investigate the potential biocontrol mechanisms of strain NJZJSB3, the nonvolatile antifungal compounds it produces were identified as iturin homologs using HPLC-ESI-MS. Antifungal volatile organic compounds were identified by gas chromatography-mass spectrometry. The detected volatiles toluene, phenol, and benzothiazole showed antifungal effects against S. sclerotiorum in chemical control experiments. Strain NJZJSB3 also produced biofilm, siderophores and cell-wall-degrading enzymes (protease and ${\beta}$-1,3-glucanase). These results suggest that strain NJZJSB3 can be a tremendous potential agent for the biological control of sclerotinia stem rot.

• The Korean Journal of Mycology
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• v.37 no.2
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• pp.181-188
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• 2009

A Gram-positive, rod-shaped bacteria named DY5 was isolated from a peat sample collected from Daeam mountain in Korea. The culture filtrate of the bacterial isolate DY5 showed a broad spectrum of antifungal activity on various crop pathogenic fungi such as Trichoderma koningii, Fusarium oxysporum, Colletotrichum gloeosporioides, Sclerotinia sclerotiorum, Rhizoctonia solani AG-1(IA) For the identification of the DY5, morphological, biochemical, API 50 CHB test, analysis of fatty acid and molecular phylogenetic approaches were performed. The DY5 was found to be a member of the genus Paenibacillus on the basis of morphological and biochemical analysis. The 16S rRNA of DY5 showed high similarity(98%) with Paenibacillus polymyxa. On the basis of these results, the DY5 was identified as Paenibacillus polymyxa. Antifungal substance of the DY5 would be mild alkaline proteine molecule. The DY5 seems to have a great potential to be a biocontrol agent against various crop pathogens.

• The Plant Pathology Journal
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• v.35 no.2
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• pp.137-148
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• 2019

In search of an effective biological control agent against the tomato pathogen Fusarium oxysporum f. sp. lycopersici, rhizospheric soil samples were collected from eight agro-ecological zones of Bangladesh. Among the bacteria isolated from soil, 24 isolates were randomly selected and evaluated for their antagonistic activity against F. oxysporum f. sp. lycopersici. The two promising antagonistic isolates were identified as Brevundimonas olei and Bacillus methylotrophicus based on morphological, biochemical and molecular characteristics. These two isolates were evaluated for their biocontrol activity and growth promotion of two tomato cultivars (cv. Pusa Rubi and Ratan) for two consecutive years. Treatment of Pusa Rubi and Ratan seeds with B. olei prior to inoculation of pathogen caused 44.99% and 41.91% disease inhibition respectively compared to the untreated but pathogen-inoculated control plants. However, treatment of Pusa Rubi and Ratan seeds with B. methylotrophicus caused 24.99% and 39.20% disease inhibition respectively. Furthermore, both the isolates enhanced the growth of tomato plants. The study revealed that these indigenous bacterial isolates can be used as an effective biocontrol agent against Fusarium wilt of tomato.

• Mycobiology
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• v.47 no.1
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• pp.126-133
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• 2019

Isaria javanica pf185 is an important entomopathogenic fungus with potential for use as an agricultural biocontrol agent. However, the effect of I. javanica pf185 on plant growth is unknown. Enhanced tobacco growth was observed when tobacco roots were exposed to spores, cultures, and fungal cell-free culture supernatants of this fungus. Tobacco seedlings were also exposed to the volatiles of I. javanica pf185 in vitro using I-plates in which the plant and fungus were growing in separate compartments connected only by air space. The length and weight of seedlings, content of leaf chlorophyll, and number of root branches were significantly increased by the fungal volatiles. Heptane, 3-hexanone, 2,4-dimethylhexane, and 2-nonanone were detected, by solid-phase micro-extraction and gas chromatography-mass spectrophotometry, as the key volatile compounds produced by I. javanica pf185. These findings illustrate that I. javanica pf185 can be used to promote plant growth, and also as a biocontrol agent of insect and plant diseases. Further studies are necessary to elucidate the mechanisms by which I. javanica pf185 promotes plant growth.

• Mycobiology
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• v.38 no.4
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• pp.286-294
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• 2010

Epicoccum purpurascens stain 5615 AUMC was investigated for its biocontrol activity against root rot disease caused by Pythium irregulare. E. purpurascens greenhouse pathogenicity tests using three leguminous plants indicated that the fungus was nonpathogenic under the test conditions. The germination rate of the three species of legume seeds treated with a E. purpurascens homogenate increased significantly compared with the seeds infested with P. irregulare. No root rot symptoms were observed on seeds treated with E. purpurascens, and seedlings appeared more vigorous when compared with the non-treated control. A significant increase in seedling growth parameters (seedling length and fresh and dry weights) was observed in seedlings treated with E. purpurascens compared to pathogen-treated seedlings. Pre-treating the seeds with the bioagent fungus was more efficient for protecting seeds against the root rot disease caused by P. irregulare than waiting for disease dispersal before intervention. To determine whether E. purpurascens produced known anti-fungal compounds, an acetone extract of the fungus was analyzed by gas chromatography mass spectrometry. The extract revealed a high percentage of the cinnamic acid derivative (trimethylsiloxy) cinnamic acid methyl ester. The E. purpurascens isolate grew more rapidly than the P. irregulare pathogen in a dual culture on potato dextrose agar nutrient medium, although the two fungi grew similarly when cultured separately. This result may indicate antagonism via antibiosis or competition.