• Research in Plant Disease
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• v.18 no.2
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• pp.109-116
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• 2012

A bacterial strain antagonistic to some fungal phytopathogens was isolated from the stem of a Persimmon tree in Yeongam, Korea. This bacterium was identified as Bacillus subtilis by 16S rRNA gene sequencing and designated as B. subtilis GDYA-1. In in vivo experiment, the fermentation broth exhibited antifungal activities against Magnaporthe oryzae on rice plants, Phytophthora infestans on tomato plants, and Puccinia recondita on wheat plants. We isolated one antifungal compound and its chemical structure was determined by mass and $^1H$-NMR spectral data. The antifungal substance was identified as benzoic acid. It inhibited mycelial growth of M. oryzae, Rhizoctonia solani, Sclerotinia sclerotiorum, and P. capsici with minimum inhibition concentration (MIC) values, ranging from 62.5 to 125 ${\mu}g/ml$. Moreover, the substance effectively suppressed Phytophthora blight of red pepper caused by P. capsici in a pot experiment. To the author's knowledge, this is the first report on the antifungal activity of benzoic acid against phytopathogenic fungi. Benzoic acid and B. subtilis GDYA-1 may contribute to environmental-friendly protect crops from phytopathogenic fungi.

• Research in Plant Disease
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• v.15 no.3
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• pp.222-229
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• 2009

A Pseudomonas strain SG3 producing biosurfactant and showing antifungal and insecticidal activities was isolated from agricultural soil severely contaminated with machine oils. The antagonistic bacterium inhibited mycelial growth of all of the tested fungal pathogens. The fermentation broth of SG3 also effectively suppressed the development of various plant diseases including rice blast, tomato gray mold, tomato late blight, wheat leaf rust, barley powdery mildew and red pepper anthracnose. An antifungal substance was isolated from the fermentation broth of SG3 by ethyl acetate partitioning, silica gel column chromatography and preparative HPLC under the guide of bioassay. The chemical structure of the antifungal substance was determined to be rhamnolipid B by mass and NMR spectral analyses. The antifungal biosurfactant showed a potent in vivo antifungal activity against gray mold and late blight on tomato plants. In addition, rhamnolipid B inhibited mycelial growth of B. cinerea causing tomato gray mold and zoospore germination and mycelial growth of P. infestans causing tomato late blight. Pseudomonas sp. SG3 producing rhamnolipid B could be used as a new biocontrol agent for the control of plant diseases occurring on tomato plants.

• The Plant Pathology Journal
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• v.26 no.4
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• pp.360-366
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• 2010

In the course of a searhing environmental friendly antifungal compounds, we found that mixture of methyl esters of fatty acids obtained from soybean oil had potent control efficacy against barley powdery mildew (Blumeria graminis f. sp. hordei). In this study, ten alkyl fatty acid esters (AFAEs) were tested for in vivo antifungal activity against five plant diseases such as rice blast, rice sheath blight, tomato gray mold, tomato late blight and barley powdery mildew. Some AFAEs showed the most control efficacy against barley powdery mildew among the tested plant diseases. By 5-hr protective and 1-day curative applications, six AFAEs ($3,000\;{\mu}g/ml$), including methyl and ethyl palmitates, methyl and ethyl oleates, methyl linoleate, and methyl linolenate demonstrated both curative and protective activities against barley powdery mildew. In contrary, methyl laurate strongly controlled the development of powdery mildew on barley plants by curative treatment at a concentration of $333\;{\mu}g/ml$, but did not show protective activity even at $3,000\;{\mu}g/ml$. Under greenhouse conditions, the seven AFAEs ($1,000\;{\mu}g/ml$) except for methyl and ethyl stearates, and methyl caprylate also effectively controlled cucumber powdery mildew caused by Podosphaera xanthii. Among them, methyl and ethyl palmitates ($333\;{\mu}g/ml$) represented the most control activity of more than 68% against the disease. The results are the first report on the antifungal activity of methyl and ethyl esters of fatty acids against plant pathogenic fungi.

• YAKHAK HOEJI
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• v.40 no.5
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• pp.608-615
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• 1996

6-[(N-3,4-Difluorophenyl)amino]-7-chloro-5,8-quinolinedione(RCK4) was tested for antifungal activities, against systemic infections with Candida albicans in normal mice. The therapeutic potential of RCK4 had been assessed in comparison with ketoconazole and fluconazole. RCK4 had $ED_{50},\;0.30{\pm}0.14$ but ketoconazole and fluconazole had $ED_{50},\;8.00{\pm}0.73,\;10.00{\pm} 0.43mg/kg$ respectively. Intraperitoneally administered RCK3 at the $ED_{50}$ for 7 days and 14 days reduced Candida albicans colony count in the kidneys and liver as well as ketoconazole and fluconazole at these $ED_{50}$. And administered RCK4 at the $ED_{50}$ for 14 days improved survival rates as well as ketoconazole. Acute oral toxicity studies of RCK4 were carried out in ICR mice of both sexes. These acute oral toxicities of RCK4 were low and $LD_{50}$ values were over 2,850mg/kg in ICR mice. The genotoxicities of RCK4 had been evaluated. RCK4 was negative in Ames test with Salmonella typhimurium and chromosomal aberration test in CHL cells. The clastogenicity was tested on the RCK4 with in vivo mouse micronucleus assay. RCK4 did not show any clastogenic effect in mouse peripheral blood and was negative in mouse micronucleus assay. These results indicate that RCK4 has no genotoxic potential under these experimental conditions.

• Journal of Microbiology and Biotechnology
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• v.13 no.3
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• pp.415-421
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• 2003

A bacterium, Pseudomonas fluorescens 2112, that is antagonistic against a red-pepper blight-causing fungus, Phytophthora capsici, was isolated from the local soil of Gyongju, Korea. This strain formed an orange-colored clear halo zone on chrome azurol S (CAS) blue agar, suggesting the production of a siderophore in addition to an antifungal antibiotic. The optimal culture conditions for siderophore production by P. fluorescens 2112 were 30-h cultivation at $25^{\circ}C$ and pH 6.5 in King's B medium. The presence of $20{\mu}g/ml\;of\;Fe^3+$ ion or EDDHA promoted the production of siderophore in King's B medium. The siderophore was purified from culture broth by CM-Sephadex C-25 and Sephadex G-25 column chromatographies. The UV spectra of the purified siderophore was the same as that of pyoverdins or pseudobactins. The molecular mass was 1,958 Da determined by FAB-rlass spectrometer, and the amino acid composition analysis showed that the purified siderophore consisted of glycine/threonine/serine/glutamic acid/alanine/lysine with the molar ratio of 3:2:1:1:1:1, DL-Threo-${\beta}$-hydroxyaspartic acid and $N^{\delta}$-hydroxyornithine, two of the essential constituents of pyoverdin, were also found. The purified siderophore pyoverdin showed strong in vitro and in vivo antagonistic activities against phytophthora blight-causing P. capsici. Especially in an in vivo pot test, the siderophore protected red-pepper Capsicum annum L. very well from the attack of P. capsici. These results indicated that the purified siderophore of P. fluorescens 2112 played a critical role in the biocontrol of the red-pepper blight disease, equivalent to treatment by P.fluorescens 2112 cells.

• Applied Biological Chemistry
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• v.41 no.6
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• pp.471-476
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• 1998

A synthesis and the screening of new 2-iminothiazolines (IV) of which structures are modified based on a lead compound, thiazoline for development of new agrochemical fungicide were described. Bromination of acetoacetanilides (I) which were prepared by the reaction of diketene with anilines gave the corresponding ${\gamma}-bromoacetoactanilide\;(II)$. Treatment of II with N-phenyl-N'-methyl thiourea (III) afforded IV, structure of which was confirmed by various spectroscopic methods. Antifungal activity of the new IV was tested against six kinds of typical plant diseases (in vivo). The IV with aromatic substituents showed remarkable activity against the Pyricuraria oryzae at 250 ppm in primary screening. The candidates with control value over 90% in primary screening were selected and further tested for second screening at lower concentrations. The IV which has an electron-withdrawing substituent such as halogen, especially fluorine in aryl group showed a higher activity as compared to those with electron-donating group and meta substituent was for optimal position.

• Korean Journal of Medicinal Crop Science
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• v.6 no.4
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• pp.277-285
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• 1998

Antifungal activity on major seedborne diasease of crops was screened by the treatment of the extracts from 50 medicinal plants in vitro and in vivo. The extracts of garlic and taxus, Rheum undulatum, Achiranthes japonica, Glycyrrhiza uralensis, Oenothera lamar kiana treated with the blotting filter paper and water agar methods inhibited the growth of Pyricularia oryzae, Alternaria sesamicola, Colletotrichum gloeosporioides, and Alternaria brassicicola among the tested plants. Antifungal activities on infected seeds by soaking methods were shown even at the dilution of the extracts by 10 times. The activity was the highest in soaking seeds at $25^{\circ}C$ for 24 hours. The effect of plant extract on seed germination was not significant as compared with untreated seed. However, early growth of seedling was increased by the treatment of extracts. The extract of taxus slightly inhibited the seed germination of radish and chinese cabbage but those of Achirunthes japonica, Glycyrrhiza uralensis and Oenthfera lamarkiana showed severe damage on the seed germination and early growth of seedling.

• The Korean Journal of Pesticide Science
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• v.12 no.4
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• pp.307-314
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• 2008

Sixty compounds such as alkylphenyl fluorobenzoate esters from thymol(I), 5-isopropyl-3-methylphenol (II), 4-isopropyl-3-methylphenol (III), 2-sec-butylphenol (IV) and 4-sec-butylphenol (V) were synthesized. These derivatives were identified by IR, $^1H$-NMR spectrometer and GC/MS. Their in vivo antifungal activities were tested against phytopathogens such as Phytophthora infestans, Botrytis cinerea, Colletotrichum orbiculare and Rhizoctonia solani. As the result, 2-sec-butylphenyl 2,5-difluorobenzoate (IV-6) and 4-sec-butylphenyl 2,5-difluorobenzoate (V-6) showed 90% above antifungal activity against Botrytis cinerea. 2-Isopropyl-5-methylphenyl 2,3,6-trifluorobenzoate (I-11), 2-isopropyl-5-methylphenyl 2,4,5-trifluorobenzoate (I-12), 5-isopropyl-3-methylphenyl 2,3,6-trifluorobenzoate (II-11), 4-isopropyl-3-methylphenyl 2,3,6-trifluorobenzoate (III-11) and 4-isopropyl-3-methylphenyl 2,4,5-trifluorobenzoate (III -12) showed 90% above potent antifungal activity against Colletotrichum orbiculare.

• Mycobiology
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• v.39 no.1
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• pp.26-32
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• 2011

Powdery mildew is one of the most devastating diseases in cucurbits. Crop yield can decline as the disease severity increases. In this study, we evaluated the effect of silver nanoparticles against powdery mildew under different cultivation conditions in vitro and in vivo. Silver nanoparticles (WA-CV-WA13B) at various concentrations were applied before and after disease outbreak in plants to determine antifungal activities. In the field tests, the application of 100 ppm silver nanoparticles showed the highest inhibition rate for both before and after the outbreak of disease on cucumbers and pumpkins. Also, the application of 100 ppm silver nanoparticles showed maximum inhibition for the growth of fungal hyphae and conidial germination in in vivo tests. Scanning electron microscope results indicated that the silver nanoparticles caused detrimental effects on both mycelial growth and conidial germination.

• The Plant Pathology Journal
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• v.28 no.3
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• pp.317-321
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• 2012

Plants are the promising reservoirs for natural products with their diverse secondary metabolites. Many invasive plants have been introduced in Korea, which adversely affect on the native ecosystem but holds difficulty removing them due to their proliferation. In this study, we evaluated disease control efficacy of methanol extracts from four invasive plant species against 7 representative crop pathogens. Methanol extract of Phytolacca americana effectively suppressed rice blast, tomato gray mold, and tomato late blight in a dose dependent manner. The methanol extract of Amorpha fruticosa also exhibited potent antifungal activity against pepper anthracnose in a concentration dependent way. These data suggest that the extracts of P. americana and A. fruticosa can be developed as plant disease protection agents against rice blast, tomato gray mold, tomato late blight, and pepper anthracnose. Furthermore, more extensive research will be required to identify and isolate active compounds from problematic invasive plant species to develop valuable agrochemicals.