• The Korean Journal of Mycology
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• v.32 no.1
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• pp.31-38
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• 2004

An endophytic bacterial strain EB215 that was isolated from cucumber (Cucumis sativus) roots displayed a potent in vivo antifungal activity against Colletotrichum species. The strain was identified as Burkholderia cepacia based on its physiological and biochemical characteristics, and 16S rDNA gene sequence. Optimal medium and incubation period for the production of antifungal substances by B. cepacia EB215 were nutrient broth (NB) and 3 days, respectively. An antifungal substance was isolated from the NB cultures of B. cepacia EB215 strain by centrifugation, n-hexane partitioning, silica gel column chromatography, preparative TLC, and in vitro bioassay. Its chemical structure was determined to be pyrrolnitrin by mass and NMR spectral analyses. Pyrrolnitrin showed potent disease control efficacy of more than 90% against pepper anthracnose (Colletotrichum coccodes), cucumber anthracnose (Colletotrichum orbiculare), rice blast (Magnaporthe grisea) and rice sheath blight (Corticium sasaki) even at a low concentration of $11.1\;{\mu}g/ml$. In addition, it effectively controlled the development of tomato gray mold (Botrytis cinerea) and wheat leaf rust (Puccinia recondita) at concentrations over $33.3\;{\mu}g/ml$. However, it had no antifungal activity against Phytophthora infestans on tomato plants. Further studies on the development of microbial fungicide using B. cepacia EB215 are in progress.

• The Korean Journal of Mycology
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• v.32 no.1
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• pp.8-15
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• 2004

This study was conducted to discover new phytotoxins which may be used as lead molecules for the development of new herbicides. A total of 187 endophytic fungi were isolated from 11 plant species, which were collected from 8 locations in Korea. Their herbicidal activities were screened in vivo by herbicidal and duckweed bioassays after they were cultured in potato dextrose broth and rice solid media. Both fermentation broth and solid culture extract of Gliocladium catenulatum F0006 isolated from red pine (Pinus densiflora) showed 70% herbicidal activity only against cocklebur (Xanthium strumarium) out of the 10 weeds tested. Solid culture extract of F0034 isolated from arrowroot (Pueraria thunbergiana) exhibited 20 to 100% herbicidal activities against all of the weeds. Especially, shattercane (Sorghum bicolor), barnyardgrass (Echinochloa crus-galli), large crabgrass (Digitaria sanguinalis), and fall pauicum (Panicum dichtomiflorum) were sensitive to the solid culture extract of F0034. In addition, solid culture extract of F0043 isolated from red pine displayed 20% to 70% herbicidal activities only against 5 grass species, but not against 5 broad-leaf plant species. On the other hand, as the results of duckweed assay, 8 fermentation broths showed 100% growth inhibitory activity at concentrations less than 5.0% of culture supernatants and 12 solid cultures had a potent inhibitory activity against duckweed growth. A toxic metabolite was purified from the solid cultures of G. catenulatum F0006 by repeated column chromatography and bioassay. It caused a phytotoxic syndrome only on cocklebur out of the 10 weeds tested; it completely killed cocklebur seedlings at $500\;{\mu}g/ml$ and showed 85% herbicidal activity against cocklebur at $100\;{\mu}g/ml$. The molecular weight of the toxic metabolite is 238 daltons and its structure determination is underway.

• Research in Plant Disease
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• v.21 no.4
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• pp.290-296
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• 2015

This study was conducted to establish an efficient screening system for resistant tomato to bacterial wilt caused by Ralstonia solanacearum. Under several conditions such as inoculation methods, growth stages of tomato seedlings, inoculum concentrations, and incubating temperatures after inoculation, development of bacterial wilt on nine resistant or susceptible cultivars of tomato was investigated. To inoculate by drenching the non-cut roots with the bacterial suspension was better to distinguish resistance and susceptibility of tomato cultivars than by drenching the cut roots using scalpel. And 'Hawaii7996' a resistant tomato to R. solanacearum showed high resistance at all the tested conditions including growth stages (3-, 6-, 8-, 10-leaf stages), inoculum concentrations ($OD_{600}=0.1-0.4$) and incubation temperatures (25, 30, $35^{\circ}C$). On the other hands, susceptible cultivars represented disease index of 3.7 and 3.9 at 6- and 8-leaf stages, respectively. At 3- and 10-leaf stages, the cultivars demonstrated lower disease severity of 2.1 and 0.5, respectively, than at 6- and 8-leaf stages. When the inoculated seedlings were incubated in growth chambers of 25, 30 and $35^{\circ}C$, disease severity of susceptible cultivars was significantly greater at 30 and $35^{\circ}C$ than at $25^{\circ}C$. In addition, the level of resistance of the tomato cultivars was not significantly affected by inoculum concentrations of $OD_{600}=0.1-0.4$. On the basis of the results, we suggest an efficient screening method to measure resistance level of tomato cultivars to bacterial wilt. The eight-leaf stage seedlings transplanted 7 days before inoculation, are inoculated with R. solanacearum by drenching the non-cut roots with a bacterial suspensions ($OD_{600}=0.4$) to give inoculum volume of 50 ml/soil l. The inoculated plants are incubated in a growth room at $30^{\circ}C$ for 12-13 days with 12-hour light a day.

• Research in Plant Disease
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• v.20 no.4
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• pp.235-244
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• 2014

Clubroot and Fusarium wilt of cole crops (Brassica oleracea L.) are destructive diseases which for many years has brought a decline in quality and large losses in yields all over the world. The breeding of resistant cultivars is an effective approach to reduce the use of chemical fungicides and minimize crop losses. This study was conducted to evaluate the resistance of 60 cabbage (B. oleracea var. capitata) and 6 broccoli (B. oleracea var. italica) lines provided by The RDA-Genebank Information Center to clubroot and Fusarium wilt. To investigate resistance to clubroot, seedlings of the genetic resources were inoculated with Plasmodiophora brassicae by drenching the roots with a mixed spore suspension (1 : 1) of two isolates. Of the tested genetic resources, four cabbage lines were moderately resistant and 'K166220' represented the highest resistance to P. brassicae. The others were susceptible to clubroot. On the other hand, to select resistant plants to Fusarium wilt, the genetic resources were inoculated with Fusarium oxysporum f. sp. conglutinans by dipping the roots in spore suspension of the fungus. Among them, 17 cabbage and 5 broccoli lines were resistant, 16 cabbage lines were moderately resistant, and the others were susceptible to Fusarium wilt. Especially, three cabbage ('IT227115', 'K161791', 'K173350') and two broccoli ('IT227100', 'IT227099') lines were highly resistant to the fungus. We suggest that the resistant genetic resources can be used as a basic material for resistant B. oleracea breeding system against clubroot and Fusarium wilt.

• Microbiology and Biotechnology Letters
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• v.33 no.1
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• pp.16-23
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• 2005

In order to develop a new microbial fungicide using endophytic bacteria for the control of anthracnoses occurring on various crops, a total of 260 bacterial strains were isolated from fresh tissues of 5 plant species. After they were cultured in broth medium, their antifungal activities were tested for in vivo antifungal activity against cucumber anthracnose caused by Colletotrichum orbiculare. As the results, liquid cultures of 28 strains showed potent antifungal activities more than $90\%$ against cucumber anthracnose. At 3-fold dilutions of liquid cultures, 18 strains inhibited the development of cucumber anthracnose of more than $70\%$. They were further tested for in vivo antifungal activity against red pepper anthracnose caused by C. coccodes and in vitro antifungal activity against C. acutatum, a fungal agent causing red pepper anthracnose. Among 18 strains, a bacterial strain EB215 isolated from cucumber roots displayed the most potent antifungal activity against Colletotrichum species. It was identified as Burkholderia cepacia based on its physiological and biochemical characteristics, Biolog test and 16S rDNA gene sequence. It also controlled effectively the development of rice blast (Magnaporthe grisea), rice sheath blight (Corticium sasaki), tomato gray mold (Botrytis cinerea), and tomato late blight (Phytophthora infestans). Studies on the characterization of antifungal substances produced by B. cepacia EB215 are in progress.

• Horticultural Science & Technology
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• v.32 no.2
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• pp.217-226
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• 2014

Root-knot symptoms were found on a commercial tomato cultivar carrying Mi, a resistance gene to root-knot nematodes including Meloidogyne incognita, M. arenaria, and M. javanica in 2012 at Buyeo, Chungnam Province in Korea. The isolate was identified as M. incognita based on molecular analyses using two species-specific primer sets. Pathogenicity of the isolate on one susceptible and three resistant tomato cultivars to the root-knot nematodes was tested. The nematode isolate showed strong pathogenicity on all the tested cultivars at all tested incubation temperatures. In addition, resistance degree of 33 commercial tomato cultivars, 8 susceptible and 25 resistant cultivars to root-knot nematodes, was also tested. Plants were determined as resistant when they suppressed the nematode reproduction. All the cultivars demonstrated strong susceptibility to the nematode regardless of resistance of the tomato cultivars. To our knowledge, this is the first report on the occurrence of Mi infecting M. incognita isolate in Korea. On the other hand, to construct an efficient screening method for selecting resistant breeding source to the nematode isolate, root-knot development of M. incognita on four tomato cultivars according to several conditions such as inoculum concentration, plant growth stage, and incubation period after transplant was investigated. Reproduction of the nematode on all the tested cultivars according to inoculum concentration increased in a dose-dependent manner. Except for inoculum concentration, there was no significant difference in reproduction level of the cultivars according to the other tested conditions. On the basis of the results, we suggest an efficient screening method for new resistant tomato to the nematode isolate.

• The Korean Journal of Pesticide Science
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• v.7 no.4
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• pp.302-309
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• 2003

Disease control activities of 230 triazolyl quinoline derivatives were investigated against six plant diseases such as rice blast, rice sheath blight, tomato gray mold, tomato late blight, wheat leaf rust (WLR) and barley powdery mildew (BPM). New triazolyl quinolines, KSI-4315 and KSI-4317 exhibited a great in vivo control activities against WLR and BPM, and then were selected for further tests such as preventive, curative, systemic, and persistence against WLR and BPM. The KSI-4315 and KSI-4317 contained MeS moiety and MsO moiety in carbon 4-position, respectively. They possessed both preventive activity and curative activity against WLR and BPM. KSI-4317 showed the better control activity than KSI-4315 against BPM, while KSI-4315 represented the better antifungal activity against WLR. Good persistence of KSI-4315 and KSI-4317 were also observed against WLR and BPM. Persistence of KSI-4315 was similar to that of KSI-4317 on WLR, but KSI-4317 was superior to KSI-4315 on BPM in its persistence. Systemic disease control of KSI-4315 and KSI-4317 was investigated by examining translaminar activity from leaf-under-surface to leaf-upper-surface, systemic activities by leaf to leaf movement and the effect of drenching treatment. Systemicities of KSI-4315 and KSI-4317 were not observed in wheat, but KSI-4317 showed more predominant systemicity than KSI-4315 in barley. These results suggest that KSI-4317 would potentially control WLR and BPM in the fields.

• Research in Plant Disease
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• v.22 no.4
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• pp.227-235
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• 2016

Plant disease caused by root-knot nematode is a major problem in crop production. Using of chemical pesticides, one of the most efficient methods to control nematodes, have raised issues in toxicity to humans and animals and environmental pollution. In this study, to select actinomycete strains that have potential to serve as a microbial agent for control of nematodes, we investigated nematicidal activity of culture broth from 670 Streptomyces isolates. A culture filtrate of KRA15-528 isolate that was identified as S. flavogriseus on the basis of 16S rRNA sequence analysis, showed strong nematicidal activity against second stage of juveniles of Meloidogyne incognita and inhibited egg hatching; exposure to 10% of culture filtrate resulted in 71% juvenile mortality at 48 hours afters treatment and suppressed egg hatching by 54% at 9 days after treatment. When the KRA15-528 culture filtrate was partitioned with ethyl acetate and butanol, ethyl acetate layer exclusively showed strong activity; 91%, 53%, 30% of mortality at 1,000, 500, $250{\mu}g/ml$, respectively. Additionally, the culture filtrate suppressed gall formation on cucumber plant by M. incognita with no phytotoxicity. These results suggest that S. flavogriseus KRA15-528 has potential to serve as a microbial nematicide for the control of root-knot nematode disease.

• Horticultural Science & Technology
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• v.35 no.2
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• pp.210-219
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• 2017

This study was conducted to establish an efficient screening method for radish (Raphanus sativus) cultivars that are resistant to black spot, which is caused by Alternaria brassicicola. Seven A. brassicicola isolates were selected and investigated for their ability to produce spores and pathogenicity. Of these isolates, A. brassicicola KACC 40036 and 43923 produced abundant spores in V-8 juice agar medium and showed pathogenicity and strong virulence on radish seedlings. We examined the resistance of 61 commercial cultivars of radish to A. brassicicola KACC40036, and found that there are no highly resistant radish cultivars; however, some cultivars, such as 'Geumbong' and 'Searom', showed weak resistance to A. brassicicola. For further study, we selected four radish cultivars that showed different disease responses to A. brassicicola KACC40036. According to the growth stage of the radish seedlings, inoculum concentration, and incubation temperature of radish, development of black spot on four cultivars has been investigated. The results showed that younger seedlings were more sensitive to A. brassicicola than older seedlings, and the disease severity depended on the concentration of the spore suspension. The disease severity of plants incubated in humidity chamber at $25^{\circ}C$ was greater than that of plants grown at $20^{\circ}C$ or $30^{\circ}C$. Taken together, we suggest the following method for screening for radish plants that are resistant to A. brassicicola: 1) inoculate 16-day-old radish seedlings with an A. brassicicola spore suspension ($2.0{\times}10^5spores{\cdot}mL^{-1}$) using the spray method, 2) incubate the inoculated plants in a humidity chamber at $25^{\circ}C$ for 24 h and then transfer the plants to a growth chamber at $25^{\circ}C$ with 80% relative humidity under a 12 h light/dark cycle, and 3) assess the disease severity of the plants two days after inoculation.

• The Korean Journal of Pesticide Science
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• v.8 no.4
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• pp.338-346
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• 2004

The methanol extract of Chloranthus japonicus roots effectively controlled the development of rice blast(Magnaporthe grisea), rice sheath blight(Corticium sasaki), tomato pay mold(Btrytis cinerea), tomato late blight(Phytophthora infestans), and wheat leaf rust(Puccinia recondita). From the methanol extract of C. japonicus roots, three antifungal substances were isolated. Their chemical structures were determined to be shizukanols B, C, and D mainly by mass and NMR spectral data. Among the three substances, shizukanol C showed the strongest inhibitory activity against mycelial growth of the plant pathogenic fungi tested; it completely inhibited mycelial growth of M. grisea. Colletotrichum gloeosporioides, and C. acutatum at concentrations of more than $12.5{\mu}g$/ and P. infestans at concentrations of more than $3.13{\mu}g/m\ell$. They also controlled effectively the development of rice blast and wheat leaf rust. On the other hand, they caused phytotoxic symptoms on barley leaves and inhibited the growth of duckweed (Lemna paucicostata) with $EC_{50}$ values of $30.0{\mu}g/m\ell$ for shizukanol B, $49.9{\mu}g/m\ell$ for shizukanol C, and $154{\mu}g/m\ell$ for shizukanol D. In addition, shizukanol C showed an insecticidal activity against brown planthopper (Nilaparavata lugens), peen peach aphid (Myzus persicae), diamond-back moth (Plutella xylostella), and tobacco cutworm (Spodoptera litura) of the 5 arthropod pests tested with mortality values of more than 60% at a concentration of $1,000{\mu}g/m\ell$.