• The Plant Pathology Journal
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• 제35권1호
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• pp.19-31
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• 2019

Bud rot (BR) is the most devastating disease affecting oil palm (Elaeis guineensis) crops in Colombia. Its causal agent, Phytophthora palmivora, initiates the infection in immature oil palm leaflets producing necrotic lesions, followed by colonization of opportunistic necrotrophs, which increases disease damage. To improve the characterization of the disease, we transformed P. palmivora using Agrobacterium tumefaciens-mediated transformation (ATMT) to include the fluorescent proteins CFP-SKL (peroxisomal localization), eGFP and mRFP1 (cytoplasmic localization). The stability of some transformants was confirmed by Southern blot analysis and single zoospore cultures; additionally, virulence and in vitro growth were compared to the wild-type isolate to select transformants with the greatest resemblance to the WT isolate. GFP-tagged P. palmivora was useful to identify all of the infective structures that are commonly formed by hemibiotrophic oomycetes, including apoplastic colonization and haustorium formation. Finally, we detected cell death responses associated with immature oil palm tissues that showed reduced susceptibility to P. palmivora infection, indicating that these tissues could exhibit age-related resistance. The aim of this research is to improve the characterization of the initial disease stages and generate cell biology tools that may be useful for developing methodologies for early identification of oil palm materials resistant or susceptible to BR.

• Mycobiology
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• 제50권5호
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• pp.326-344
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• 2022

The fungal-like family Saprolegniaceae (Oomycota), also called "water mold," includes mostly aquatic saprophytes as well as notorious aquatic animal pathogens. Most studies on Saprolegniaceae have been biased toward pathogenic species that are important to aquaculture rather than saprotrophic species, despite the latter's crucial roles in carbon cycling of freshwater ecosystems. Few attempts have been made to study the diversity and ecology of Saprolegniaceae; thus, their ecological role is not well-known. During a survey of oomycetes between 2016 and 2021, we investigated the diversity and distribution of culturable Saprolegniaceae species in freshwater ecosystems of Korea. In the present study, members of Saprolegniaceae were isolated and identified at species level based on their cultural, morphological, and molecular phylogenetic analyses. Furthermore, substrate preference and seasonal dynamics for each were examined. Most of the species were previously reported as animal pathogens; however, in the present study, they were often isolated from other freshwater substrates, such as plant debris, algae, water, and soil sediment. The relative abundance of Saprolegniaceae was higher in the cold to cool season than that in the warm to hot season of Korea. This study enhances our understanding of the diversity and ecological attributes of Saprolegniaceae in freshwater ecosystems.

• Mycobiology
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• 제33권1호
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• pp.23-29
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• 2005

The effects of different concentrations of three amino acids as carbon and or nitrogen sources on mycelial dry weights, changes in pH values of synthetic medium, ammonia secretion and extracellular protease activity by three zoosporic fungi, pathogens of fish and shellfish, were studied. As compared with the control, the addition of isoleucine and aspartic acid as nitrogen sources were generally stimulative for mycelial dry weight production whereas phenylalanine was inhibitory irrespective to the tested fungal species. When amino acids served as carbon and nitrogen sources, the mycelial dry weights of the three fungi were increased (mostly non-significantly) relative to untreated control but weights were decreased as the concentrations of the three amino acids raised. The addition of individual amino acids as carbon and nitrogen sources to the medium significantly increased pH values of the medium comparable to the control. The addition of each of the three amino acids as carbon and nitrogen sources to the medium significantly induced ammonia secretion by the three species of zoosporic fungi. Ammonia secretion in synthetic medium amended with amino acids as nitrogen source raised by the three zoosporic fungi relative to untreated control except in case of Achlya racemosa treated with isoleucine. Extracellular protease activity was almost promoted in case of Achlya proliferoides and Saprolegnia furcata cultures treated with isoleucine and aspartic acid individually in presence of glucose and vice versa in case of phenylalanine. However, extracellular protease activity of A. racemosa decreased compared with the control at various concentrations of isoleucine and both phenylalanine and aspartic acid assumed inconsistent effects. Extracellular protease activity of the three zoosporic fungi in the medium devoid of glucose varied depending upon zoosporic fungal species, the tested amino acid and the applied concentrations. The values of protease activity were approximately less two folds than that obtained in presence of glucose.

• The Plant Pathology Journal
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• 제22권1호
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• pp.75-89
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• 2006

The actinomycete strain JK-1 that showed strong inhibitory activity against some plant pathogenic fungi and oomycetes was isolated from Jung-bal Mountain in Ko-yang, Korea. The strain JK-1 produced spores singly borne on sporophores and the spores were spherical and 0.9-1.2 11m in diameter. The cell wall of the strain JK-1 contained meso-diaminopimelic acid. The actinomycete strain JK-1 was identified as the genus Micromonospora based on the morphological, physiological, biochemical and chemotaxonomic characteristics. From the 168 rDNA analysis, the strain JK-1 was assigned to M aurantiaca. The antibiotic MA-1 was purified from the culture broth of M aurantiaca JK-1 using various purification procedures, such as Diaion HP20 chromatography, C18 flash column chromatography, silica gel flash column chromatography and Sephadex LH-20 column chromatography. $^{1}H-$, $^{13}C-NMR$ and EI mass spectral analysis of the antibiotic MA-1 revealed that the antibiotic MA-1 is identical to phenylacetic acid. Phenylacetic acid showed in vitro inhibitory effects against fungal and oomycete pathogens Alternaria mali, Botrytis cinerea, Magnaporthe grisea, Phytophthora capsici and yeast Saccharomyces cerevisiae at < 100 $\mug$ $ml^{-1}$. In addition, phenylacetic, acid completely inhibited the growth of Sclerotinia sclerotiorum, Bacillus subtilis, Candida albicans, Xanthomonas campestris pv. vesicatoria at < $\mug$ $ml^{-1}$. Phenylacetic acid strongly inhibited conidial germination and hyphal growth of M grisea and C. orbiculare. Phenylacetic acid showed significantly high levels of inhibitory' effect against rice blast and cucumber anthracnose diseases at 250 $\mug$ $ml^{-1}$. The control efficacies of phenylacetic acid against the two diseases were similar to those of commercial compounds tricyclazole, iprobenfos and chlorothalonil .n the greenhouse.

• The Plant Pathology Journal
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• 제28권1호
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• pp.20-31
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• 2012

Endophytic bacterial communities of tidal flat plants antagonistic to oomycete plant pathogens were studied by the isolation of 256 root colonizing endophytic bacteria from surface-disinfected root tissues of six plants ($Rosa$ $rugosa$, $Suaeda$ $maritima$, $Vitex$ $rotundifolia$, $Carex$ $scabrifolia$, $Glehnia$ $littoralis$ and $Elymus$ $mollis$) growing in a tidal flat area of Namhae Island, Korea. To understand the antagonistic potential, an $in$ $vitro$ antagonistic assay was performed to characterize and identify strains that were antagonistic to the oomycete plant pathogens $Phytophthora$ $capsici$ and $Pythium$ $ultimum$ from the total population. Nine percent of the total number of isolated bacteria exhibited in vitro inhibitory activity against target plant pathogenic oomycetes. Taxonomic and phylogenetic placement of the antagonistic bacteria was investigated by analysis of the 16S rRNA gene sequences. The sequence analysis classified the antagonistic strains into four major classes of the domain bacteria ($Firmicutes$, ${\alpha}-Proteobacteria$, ${\gamma}-Proteobacteria$ and $Actinomycetes$) and 10 different genera. Further production of secondary metabolites, hydrolytic enzymes and plant growth promoting traits were determined for the putative new species of antagonistic endophytic bacteria. These new strains could not be identified as known species of ${\alpha}-Proteobacteria$, and so may represent novel bacterial taxa. The unexpected high antagonistic bacterial diversity associated with the tidal flat plants may be indicative of their importance in tidal flat plants as a promising source of novel antimicrobial compounds and biocontrol agents.

• 한국균학회지
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• 제52권2호
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• pp.73-96
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• 2024

Root and stem rot caused by Phytophthora palmivora is one of the most serious diseases affecting durian production in Thailand where metalaxyl, an effective fungicide against oomycetes, has been used extensively for a long period to control this disease. Although field isolates of P. palmivora resistant to metalaxyl exist in Thailand, a molecular basis for P. palmivora has not yet been elucidated regarding metalaxyl resistance. The current study tested whether P. palmivora RPA1 (the DNA-directed RNA polymerase I subunit gene), a homolog gene of RPA190 associated with metalaxyl resistance in some isolates of Phytophthora infestans, had a role in the resistance mechanism toward metalaxyl. In total, 40 durian-derived isolates of P. palmivora were assessed for metalaxyl sensitivity using a mycelial growth inhibition assay. The effective concentrations for 50% mycelial growth inhibition values for all isolates tested were in the range 0.01-872.88 mg/L. The isolates were clustered into three groups: sensitive (n=23), moderately resistant (n=11), and resistant (n=6) groups. No polymorphism was revealed based on multiple alignment analysis of the amino acid sequences translated from the corresponding DNA sequences in the region of RPA1 of the metalaxyl-sensitive (n=5), moderately resistant (n=2), and resistant isolates (n=6). Furthermore, investigation of the RPA1 expression among these representative isolates (n=3, each group) indicated that RPA1 expression may not be involved in the regulation of P. palmivora resistance to metalaxyl. Based on this line of evidence, there was no detected relationship regarding metalaxyl resistance and P. palmivora RPA1.

• Applied Biological Chemistry
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• 제46권2호
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• pp.79-83
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• 2003

난균류에 속하는 Phytophthora spp.와 pythium spp.에서 분비되는 단백질인 elicitin은 식물과 병원균과의 비친화적 관계에서 과민감반응을 유도하는 인자로 알려져 왔다. 국내에서 수집된 5종의 Phytophthora spp로부터 분리된 elicitin들은 무, 배추, 고추에서 과민감 반응을 유도 하였으나 오이, 토마토에서는 볼 수 없었다. 특히 지금까지 보고가 되지않은 P. cambivora KACC 40160균주의 배양액으로부터 ion exchange와 gel filtration을 이용하여 고추에 과민감반응을 유도하며 분자량이 10kDa인 새로운 elicitin을 순수분리 하여 cambivorein이라 명명 하였다. 분리된 cambivorein의 N-말단 아미노산 서열분석 결과 ${\beta}-isoform$의 특징인 13번째 아미노산이 Iysine을 가지고 있었으며 기존의 다른 종류의 elicitin과는 다른 아미노산으로 구성되어 있었다.

• 농약과학회지
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• 제9권1호
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• pp.81-87
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• 2005

Ethaboxam[(RS)-N-(a-cyano-2-thenyl)-4-ethyl-2-(ethylamino)-1,3-thiazole-5-carboximide]은 난균강 미생물에 대하여 우수한 살균활성을 보이는 신규 살균제이다. Ethaboxam 원제와 몇 가지 ethaboxam 제형의 배추 뿌리혹병에 대한 방제효과를 조사하였다. Ethaboxam을 관주처리 하였을 때, 토양 1 L 당 8.33 mg 농도 처리구는 배추 뿌리의 혹 형성이 완전히 억제되었으며, $EC_{50}$ 값은 2.65 mg/L 토양이었다. Ethaboxam 5개 제형(10% 액상수화제, 15% 액상수화제, 2% 입제, 5% 입제, 25% 수화제) 그리고 ethaboxam과 metalaxyl 합제 제형(3%+1% 입제)의 배추 뿌리혹병 방제효과는 우수하였다. 이들 중 토양 관주처리 한 ethaboxam의 10% 및 15% 액상수화제, 토양 혼화처리 한 ethaboxam 2% 입제 제형은 다른 제형보다 배추 뿌리혹병에 대하여 더 우수한 방제효과를 보였다. 이들의 배추 뿌리혹병에 대한 $EC_{50}$ 값은 원제기준으로 토양 L 당 각각 3.72 mg(10% 액상수화제), 1.10 mg (15% 액상수화제), 4.95 mg (2% 입제) 이었다. 그러므로 실험한 ethaboxam 6개 제형 중에 15% 액상수화제가 배추 뿌리혹병에 대하여 가장 우수한 방제효과를 나타냄을 알 수 있었다. 이들 결과로부터 ethaboxam은 포장에서도 배추 뿌리혹병을 효과적으로 방제할 수 있으리라 생각되었다.