• The Plant Pathology Journal
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• 제22권4호
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• pp.364-368
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• 2006

Survival of biocontrol agents and their effective colonization of rhizhosphere are the essential components for successful disease suppression. The effects of hydrogel supplement on bacterial survival and disease control were evaluated in pot and in the field. Addition of 2% hydrogel material to potting soil resulted in significant enhancement of colonization of biocontrol agent Serratia plymuthica A21-4 both in soil and rhizosphere of pepper plants. Rhizosphere colonization of S. plymuthica A21-4 retrieved from 40 days old pepper seedlings indicated 100 times higher bacterial population in hydrogel treated soil than in ordinary pot soil. The pepper plants sown in hydrogelated potting soil showed higher seed germination rate and the better growth of pepper plant than those in ordinary commercial pot soil. Although the suppression of Phytophthora capsid density in the potting soil by treatment of biocontrol agent A21-4 was not significantly different between in hydrogelated soil and ordinary potting soil, the suppression of Phytophthora blight between two treatments was significantly different. A21-4 treatment in hydrogelated potting soil was completely disease-free while same treatment in ordinary potting soil revealed 36% disease incidence. Our field study under natural disease occurrence also showed significantly less disease incidence(12.3%) in the A21-4 treatment in the hydrogelated soil compared to other treatments. Yield promotion of pepper by the A21-4 treatment in the hydrogelated potting soil was also recognized. Our results indicated that hydrogel amendment with biocontrol agent in pot soil would be a good alternative to protect pepper seedlings and increase plant yield.

• Journal of Microbiology and Biotechnology
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• 제28권5호
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• pp.831-838
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• 2018

Trophic interactions of introduced biocontrol fungi with soil animals can be a key determinant in the fungal proliferation and activity. This study investigated the trophic interaction of an introduced biocontrol fungus with soil nematodes. The biocontrol fungus Trichoderma harzianum ThzID1-M3 and the fungivorous nematode Aphelenchoides sp. (10 per gram of soil) were added to nonsterile soil, and microbial populations were monitored for 40 days. Similar results were obtained when the experiment was duplicated. ThzID1-M3 stimulated the population growth of indigenous nematodes (p < 0.05), regardless of whether Aphelenchoides sp. was added. Without ThzID1-M3, indigenous nematodes did not increase in number and the added Aphelenchoides sp. nematodes almost disappeared by day 10. With ThzID1-M3, population growth of nematodes was rapid between 5 and 10 days after treatment. ThzID1-M3 biomass peaked on day 5, dropped at day 10, and then almost disappeared at day 20, which was not influenced by the addition of nematodes. In contrast, a large quantity of ThzID1-M3 hyphae were present in a heat-treated soil in which nematodes were eliminated. Total fungal biomass in all treatments peaked on day 5 and subsequently decreased. Addition of nematodes increased the total fungal biomass (p < 0.05), but ThzID1-M3 addition did not affect the fungal biomass. Hyphae of total fungi when homogenously distributed did not support the nematode population growth; however, hyphae of the introduced fungus did when densely localized. The results suggest that soil fungivorous nematodes are an important constraint on the hyphal proliferation of fungal agents introduced into natural soils.

• The Plant Pathology Journal
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• 제21권3호
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• pp.275-282
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• 2005

A chitinolytic bacterium, Chromobacterium sp. strain C-61, was found strongly antagonistic to Rhizoctonia solani, a causal agent of damping-off of eggplant. In this study, the biocontrol activity and enzymatic characteristics of strain C-61 were compared with its four Tn5 insertion mutants (C61-A, -B, -C, and -D) that had lower chitinolytic ability. The chitinase activity of a 2-day old culture was about $76\%,\;49\%\;and\;6\%$ level in C61-A, C61-B and in C61-C, respectively, compared with that of strain C-61. The $\beta-N-acetylhexosaminidase$(Nahase) activity was little detected in strain C-61 but increased largely in C-61A, C61-B and C61-C. Activities of chitinase and Nahase appeared to be negatively correlated in these strains. Another mutant, C-61D, produced no detectable extracellular chitinase and Nahase. The in vitro and in vivo biocontrol activities of strain C-61 and its mutants were closely related to their ability to produce chitinase but not Nahase. No significant differences in population densities between strain C-61 and its mutants were observed in soil around eggplant roots. The results of SDS-PAGE and isoelectrofocusing showed that a major chitinase of strain C-61 is 54-kDa with pI of approximately 8.5. This study provides evidence that the biocontrol activity of Chromobacterium sp. strain C-61 against Rhizoctonia solani depends on the ability to produce chitinase with molecular weight of 54-kDa and pI of 8.5.

• The Plant Pathology Journal
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• 제19권3호
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• pp.129-132
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• 2003

Fusarium wilt of cucumber caused by Fusarium oxy-sporum f. sp. cucumerinum is a serious vascular disease worldwide. Biological control of Fusarium wilt in several crops has been accomplished by introducing non-pathogenic Fusarium sup. and other biocontrol agents in soil or in infection courts. In this study, quantitative models were used to determine the biocontrol efficacy of inundatively applied antagonist formulations and the length of their effectiveness in controlling Fusarium wilt of cucumber. Quantitative model of the form [Y=L (1${-exp}^{-kx}$)] best described the relationship between disease incidence (Y, %) and inoculum density (X) of isolates F51 and F55. Isolate F51 was selected as a more virulent isolate based on the extent of its effectiveness in causing the wilt disease. The degree of disease control (Xi/X) obtained with the density of the biocontrol agent (Z), was described by the model [Xi/X=A (1${-exp}^{-cz}$)]. The zeolite-based antagonist formulation amended with chitosan (ZAC) was better at lower rates of application and peaked at around 5 g/ kg of the potting medium, whereas the peat-based antagonist formulation (PA) peaked at around 10 g/kg of the potting medium. ZAC formulation provided significantly better suppression of Fusarium wilt as described by the curvilinear relationship of the type Y= a+bX+c$X^2$, where Y represents percent disease incidence and X represents sustaining effect of the biocontrol agent.

• 식물병연구
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• 제12권3호
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• pp.267-271
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• 2006

Botrytis cinerea에 의한 포도 잿빛곰팡이병은 특히 하우스 재배시 큰 피해를 주는 병원 진균이다. Pseudomonas속 세균들은 토양 미생물중 가장 잘 연구되어 있고, 토양 내에서 중요한 역할을 담당하고 있다. 근권토양에서 분리한 형광성 Pseudomonas속 세균 83균주 중 P84균주는 실내 항균력 실험결과 다양한 식물병원진균(Phytophthora capsici, Sclerotium spp., Botryosphaeria dothidea, Fusarium spp.)에 대해 항균효과를 나타내었다. 생리적 실험과 유전적 실험결과 P84균주는 P. putida로 동정되었다. 이 세균의 항균력은 항생물질(2,4-diacetylphloroglucinol)의 생산과 관련되어 있는 것으로 사료되며, 이 세균이 포도 잿빛곰팡이병의 생물적 방제에 이용될 수 있는 가능성이 시사되었다.

• The Plant Pathology Journal
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• 제28권1호
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• pp.68-74
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• 2012

Biocontrol microbes have mainly been screened among large collections of microorganisms $via.$ nutrient-rich $in$ $vitro$ assays to identify novel and effective isolates. However, thus far, isolates from only a few genera, mainly spore-forming bacilli, have been commercially developed. In order to isolate field-effective biocontrol microbes, we screened for more than 200 oligotrophic bacterial strains, isolated from rhizospheres of various soil samples in Korea, which induced systemic resistance against the soft-rot disease caused by $Pectobacterium$ $carotovorum$ SCC1; we subsequently conducted in $planta$ bioassay screening. Two oligotrophic bacterial strains were selected for induced systemic disease resistance against the $Tobacco$ $Mosaic$ $Virus$ and the gray mold disease caused by $Botrytis$ $cinerea$. The oligotrophic bacterial strains were identified as $Pseudomonas$ $manteilii$ B001 and $Bacillus$ $cereus$ C003 by biochemical analysis and the phylogenetic analysis of the 16S rRNA sequence. These bacterial strains did not exhibit any antifungal activities against plant pathogenic fungi but evidenced several other beneficial biocontrol traits, including phosphate solubilization and gelatin utilization. Collectively, our results indicate that the isolated oligotrophic bacterial strains possessing induced systemic disease resistance could provide useful tools as effective biopesticides and might be successfully used as cost-effective and preventive biocontrol agents in the field.

• 식물병연구
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• 제23권1호
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• pp.19-34
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• 2017

유기농 및 지속 가능한 농산물에 대한 최근의 전 세계적인 수요는 농가 현장에서 사용 가능한 생물 농약의 개발 및 활용에 대한 요구가 증대되고 있다. 그러나 대부분의 생물학적 방제 방법은 실제 현장 조건에서 식물병 방제 스펙트럼이 제한적이고 효능이 높지 않다. 본 연구팀은 키틴분해 미생물과 키틴을 활용하여 적은 비용으로 방제효과가 우수한 키틴 기반 제형을 개발했다. 이 제형은 포장 조건에서 다양한 식물병을 성공적으로 방제하였다. 본 리뷰에서는 성공적인 포장 연구와 관련하여 이 제형에 함유되어 있는 키틴분해미생물들의 생태학적 측면과 생물적 방제 기작에 대해 기술하였다. 또한 현장에서 키틴분해미생물의 현장 대량 배양과 효과적인 생물학적 방제 방법을 사용하여 농민 친화적인 수단으로 확대 할 수 있는 생물적 방제 방법과 전략의 가능성에 대해 논의했다.

• Journal of Microbiology and Biotechnology
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• 제22권3호
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• pp.316-325
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• 2012

Xylanase has been used extensively in the industrial and agricultural fields. However, the low-yield production of xylanase from native species cannot meet the increasing demand of the market. Therefore, improving the heterologous expression of xylanase through basic gene optimization may help to overcome the shortage. In this study, we synthesized a high-GC-content native sequence of the thermostable xylanase gene xynB from Streptomyces olivaceoviridis A1 and, also designed a slightly AT-biased sequence with codons completely optimized to be favorable to Pichia pastoris. The comparison of the sequences' expression efficiencies in P. pastoris X33 was determined through the detection of single-copy-number integrants, which were quantified using qPCR. Surprisingly, the high GC content did not appear to be detrimental to the heterologous expression of xynB in yeast, whereas the optimized sequence, with its extremely skewed codon usage, exhibited more abundant accumulation of synthesized recombinant proteins in the yeast cell, but an approximately 30% reduction of the secretion level, deduced from the enzymatic activity assay. In this study, we developed a more accurate method for comparing the expression levels of individual yeast transformants. Moreover, our results provide a practical example for further investigation of what constitutes a rational design strategy for a heterologously expressed and secreted protein.

• Mycobiology
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• 제46권1호
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• pp.52-63
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• 2018

In our previous studies, Bacillus megaterium KU143, Microbacterium testaceum KU313, and Pseudomonas protegens AS15 have been shown to be antagonistic to Aspergillus flavus in stored rice grains. In this study, the biocontrol activities of these strains were evaluated against Aspergillus candidus, Aspergillus fumigatus, Penicillium fellutanum, and Penicillium islandicum, which are predominant in stored rice grains. In vitro and in vivo antifungal activities of the bacterial strains were evaluated against the fungi on media and rice grains, respectively. The antifungal activities of the volatiles produced by the strains against fungal development and population were also tested using I-plates. In in vitro tests, the strains produced secondary metabolites capable of reducing conidial germination, germ-tube elongation, and mycelial growth of all the tested fungi. In in vivo tests, the strains significantly inhibited the fungal growth in rice grains. Additionally, in I-plate tests, strains KU143 and AS15 produced volatiles that significantly inhibited not only mycelial growth, sporulation, and conidial germination of the fungi on media but also fungal populations on rice grains. GC-MS analysis of the volatiles by strains KU143 and AS15 identified 12 and 17 compounds, respectively. Among these, the antifungal compound, 5-methyl-2-phenyl-1H-indole, was produced by strain KU143 and the antimicrobial compounds, 2-butyl 1-octanal, dimethyl disulfide, 2-isopropyl-5-methyl-1-heptanol, and 4-trifluoroacetoxyhexadecane, were produced by strain AS15. These results suggest that the tested strains producing extracellular metabolites and/or volatiles may have a broad spectrum of antifungal activities against the grain fungi. In particular, B. megaterium KU143 and P. protegens AS15 may be potential biocontrol agents against Aspergillus and Penicillium spp. during rice grain storage.

• The Plant Pathology Journal
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• 제27권1호
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• pp.68-77
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• 2011

Fifty five species of medicinal plant materials were tested for their antifungal activity in vitro against Rhizoctonia solani AG 2-1 and Trichoderma harzianum to select plant species that can be used to improve the biocontrol efficacy of T. harzianum. Six species were effective against R. solani AG 2-1 but were also antagonistic to T. harzianum, except for Cinnamomum loureirii stem bark (CSB). CSB inhibited mycelial growth of R. solani AG 2-1 by 73.7% but showed an inhibitory effect on mycelial growth of T. harzianum by only 2.2%. Scanning electron microscophs showed that the CSB treatment resulted in deformed R. solani AG 2-1 hyphal cells, and transmission electron microscophs revealed degenerated cell structures such as degenerated cytoplasm and disentangled cell wall and the accumulation of electron-dense inclusions (asterisks) in the CSB treatment. The biocontrol efficacy of radish damping-off increased greatly following the combined treatments of T. harzianum and CSB and the combined treatment increased efficacy from 6.4-23.1% to 37.1-87.3% compared with either treatment alone. CSB did not affect T. harzianum population growth, as it was almost the same in rice-bran peat medium (culture) amended with 0.1% and 1.0% CSB powder as in non-amended medium. The formulation of T. harzianum in rice-bran peat medium amended with CSB powder reduced the severity of radish damping-off by 80.6%, suggesting that T. harzianum and CSB can be formulated as a biocontrol product for the control of R. solani AG 2-1.