• Journal of Microbiology and Biotechnology
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• v.18 no.1
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• pp.15-22
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• 2008

Four series (S, M, R, and W) of Alternaria longipes isolates were obtained based on consecutive selection with Dimethachlon (Dim) and ultraviolet irradiation. These isolates were then characterized according to their tolerance to Dim, sensitivity to osmotic stress, and phenotypic properties. All the selected Dim-resistant isolates showed a higher osmosensitivity than the parental strains, and the last generation was more resistant than the first generation in the M, R, and W series. In addition, the changes in the Dim resistance and osmotic sensitivity were not found to be directly correlated, and no distinct morphologic characteristics were found among the resistant and sensitive isolates, with the exception of the resistant isolate K-11. Thus, to investigate the molecular basis of the fungicide resistance, a group III two-component histidine kinase (HK) gene, AlHK1, was cloned from nineteen A. longipes isolates. AlHK1p was found to be comprised of a six 92-amino-acid repeat domain (AARD), HK domain, and response regulator domain, similar to the Os-1p from Neurospora crassa. A comparison of the nucleotide sequences of the AlHK1 gene from the Dim-sensitive and -resistant isolates revealed that all the resistant isolates contained a single-point mutation in the AARD of AlHK1p, with the exception of isolate K-11, where the AlHK1p contained a deletion of 107 amino acids. Moreover, the AlHK1p mutations in the isolates of each respective series involved the same amino acid substitution at the same site, although the resistance levels differed significantly in each series. Therefore, these findings suggested that a mutation in the AARD of AlHK1p was not the sole factor responsible for A. longipes resistance to dicarboximide fungicides.

• The Plant Pathology Journal
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• v.17 no.4
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• pp.205-209
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• 2001

Dicarboximide-resistant isolates of Monilinia fructicola grew readily on media amended with dicarbosimide fungicides, and showed cross-resistance to pentachlo-ronitrobenzene (PCNB). The fitness of resistant isolates was inferior to that of sensitive isolates. Mycelial growth on fungicide-free medium was not significantly different between the dicarboximide-resistant and sensitive isolates. The originally high $\textrm{EC}_{50}$ values of the resistant isolate decreased after storage for 16 weeks at $4^{\circ}$. After inoculation with the mixture of spore suspensions of resistant and sensitive isolates, the re-isolation rate of the resistant spores was significantly reduced regardless of the mixing ratio. From the results, it could be concluded that the competitive ability of the resistant isolates is inferior to the sensitive ones.

• Korean Journal Plant Pathology
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• v.10 no.3
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• pp.192-196
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• 1994

Two hundred and fourty-seven isolates of Phytophthora infestans obtained from infested potato leaves from the spring of 1991 to the fall of 1993 from potato fields in various regions of Korea were tested for their fungicides resistances. A total of 20.9% isolates were not suppressed at 50 ppm of metalaxyl in 1991, but isolates from 1993 were suppressed at 50 ppm of metalaxyl. Ten resistant isolates and 10 susceptible isolates to metalaxyl were selected and tested against oxadixyl, fosetyl-Al, and phosphorous acid. Effectiveness of these chemicals were no better than that of metalaxyl. Dimethomorph suppressed all isolates at 1 $\mu\textrm{g}$/ml suggesting that it might be a potential chemical to control Phytophthora infestans. Mating types of all isolates from diseased leaves in 1993 turned out to be A2 type.

• Research in Plant Disease
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• v.23 no.2
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• pp.150-158
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• 2017

Pear scab caused by Venturia nashicola has been reported as an important disease of pear resulting in lowering the quality of pear fruits. In this study, it was conducted to investigate the relationship between resistance of V. nashicola and mutation of ${\beta}$-tubulin gene and the fungicide resistance in field isolate group in benzimidazole fungicides. Responce of V. nashicola to carbendazim could be classified into 3 groups as sensitive that does not grow at all on PDA amended with $0.16{\mu}g/ml$ of carbendazim, low resistance that could not grow in $4.0{\mu}g/ml$ medium, and high resistance that can grow even at $100{\mu}g/ml$. Thirty isolates of V. nashicola collected from 3 regions as Wonju, Naju, and Okcheon were highly resistant to carbendazim. Analysis of the nucleotide sequence of ${\beta}$-tubulin gene of V. nashicola showed that there was no difference in the nucleotide sequence between the sensitive and the low-resistant isolate, but GAG at codon 198 (glutamic acid) was replaced with GCG (alanine) in the high-resistant isolate. Among 10 isolates obtained from the Okcheon, 5 isolates showed the substitution of glycine for glutamic acid, which were resistant to carbendazim, but more sensitive to the mixture of carbendazim and diethofencarb than others. Through these results, all isolates of V. nashicola isolated in pear orchard were found to be resistant to benzimidazoles. Also, mutants E198A and E198G at ${\beta}$-tubulin were found to be important mechanisms of V. nashicola resistance against benzimidazole fungicides.

• The Korean Journal of Pesticide Science
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• v.17 no.2
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• pp.133-139
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• 2013

To investigate the sensitivity of Sclerotium cepivorum causing garlic white rot to 5 fungicides, including prochloraz, tebuconazole, flutolanil, iminoctadine and isoprothiolane, 147 isolates isolated from infected garlics from 2008 to 2009 through a single sclerotium isolation were screened. While each mean value of $EC_{50}$ (effective concentration reducing mycelial growth by 50%) of S. cepivorum isolates collected in 2008 to each fungicide was 0.054, 0.012, 23.189, 0.901, and $21.362{\mu}g\;mL^{-1}$, that of 2009 isolates were 0.030, 0.020, 10.367, 1.684, $33.406{\mu}g\;mL^{-1}$. There was a difference in mean value of $EC_{50}$ of S. cepivorum according to regions isolated. $EC_{50}$ values of S. cepivorum isolated in Goheung to flutolanil and isoprothiolane were 14.468 and $24.653{\mu}g\;mL^{-1}$, respectively, which was lower than those of Seosan and Taeahn. Isolates from Taeahn showed the lowest $EC_{50}$ value to prochloraz as $0.008{\mu}g\;mL^{-1}$. In addition, we could not find any resistant isolates to fungicides tested. The $EC_{50}$ values in this study will be used in a fungicide resistance monitoring program to determine whether shifts in sensitivity to fungicides included into different groups are occurring in S. cepivorum populations.

• Korean Journal of Agricultural Science
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• v.19 no.2
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• pp.170-178
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• 1992

Isolates of Botrytis cinerea resistant to dicarboximide fungicides were collected from strawberry fields in greenhouses in spring and early summer of 1990. Five out of 9 isolates of B. cinera were resistant, which showed mycerial growth on PDA containing dicarboximide fungicides(procymidone and vinclozolin) with concentrations of 100, 400 and $1,600{\mu}g/ml$. The minimal inhibitory concentration(MIC) values of the dicaboximide-resistant isolates was more than $6,400{\mu}g/ml$, while that of the sensitive isolates was less than $6.25{\mu}g/ml$. The germination ratio of conidia of the resistant isolates on PDA containing procymidone and vincolozolin was more than 95%, while that of the sensitive was less than 15%. The procymidone-resistant isolates were also resistant to vinclozolin, showing cross-resistant between the fungicides, but cross-resistant was not observed between the dicarboximides and dichlofluanid. Resistance to benomyl was also found in all the dicarboximide resistant isolates. Occurrence frequency of dicarboximide-resistant isolates out of 223 isolates was about 40%. The resistant isolates were widely distributed throughout Korea.

• The Korean Journal of Pesticide Science
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• v.14 no.4
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• pp.427-432
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• 2010

Rice bakanae disease caused by Fusarium fujikuroi is one of the most serious rice diseases in Korea. From 2006 to 2009, 118 F. fujikuroi isolates were collected from various regions of rice fields in Korea. Resistance assay of 118 F. fujikuroi isolates to prochloraz, tebuconazole, and benomyl, were performed using agar dilution method. To investigate inhibitory effects of the fungicides, minimum inhibitory concentration of mycelial growth (MIC) and effective concentration inhibiting mycelial growth by 50% ($EC_{50}$) for 118 isolates were calculated using Sigmaplot 8.02 (Antro, SPSS UK, Ltd). Based on the means of $EC_{50}$ values, baseline resistance values were determined as $0.5{\mu}g{\cdot}mL^{-1}$ for prochloraz, $5.0{\mu}g{\cdot}mL^{-1}$ for tebuconazole and $2.5{\mu}g{\cdot}mL^{-1}$ for benomyl. Number of resistant isolates to each fungicide was 17, 19 and 43 for prochloraz, tebuconazole and benomyl, respectively. Furthermore, 4 isolates showed the double resistance to both prochloraz and tebuconazole, 6 isolates to prochloraz and benomyl, and 11 isolates to tebuconazole and benomyl. Isolates CF366 and LF335 isolated from Gyeongbuk province were resistant to the three fungicides tested, prochloraz, tebuconazole and benomyl.

• The Plant Pathology Journal
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• v.22 no.1
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• pp.1-6
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• 2006

The population shifts of Monilinia fructicola isolates which were resistant to the fungicide benzimidazoles were investigated in four regions of Korea from 1998 to 2000. The isolation frequency of benzimidazole-resistant isolates ranged from 18.8% to 29.6% in Chongdo and from $22.0\%$ to $26.8\%$ in Gyeongsan during the same period. However, the frequency of benzimidazoleresistant isolates was less than $4.0\%$ in Chochiwon and Youngduk during the same period. Benzimidazoleresistant isolates showed cross-resistance among benzimidazoles. On the other hand, none of the isolates showed cross-resistance to diethofencarb and carbendazim. Regardless of the year, the benzimidazole-resistant isolates of $EC_{50}$ higher than 500 $\mug%$ a.i./ml were isolated more frequently in mid and late season than in early season. In an orchard of Gyeongsan that had not been exposed to any fungicides for several years, the population of benzimidazole-resistant isolate had persisted without much fluctuation for three years. These results suggest that benzimidazole resistance of M. fructicola is becoming a problem in controlling brown rot and blossom blight of peach in regions like Chongdo and Gyeongsan.

• The Plant Pathology Journal
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• v.25 no.4
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• pp.317-321
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• 2009

Sensitivity to the new carboxylic acid amide fungicide, mandipropamid, of Phytophthora capsici causing pepper Phytophthora blight was determined on 187 isolates collected in Korea over 3 years, from 2005 to 2007. All isolates were sensitive to mandipropamid, with $EC_{30}$ values for growth of mycelia ranging from 0.001 to $0.037\;{\mu}g/ml$. Among the isolates, 147 (79.0%) isolates were sensitive to metalaxyl, whereas others were resistant to this fungicide. Mandipropamid had the same effect on mycelium growth of both metalaxyl-sensitive and metalaxyl-resistant isolates, indicating an absence of cross-resistance between these two fungicides. Comparison of the sensitivities of P. capsici isolates showed a positive correlation between sensitivity to mandipropamid and dimethomorph ($r^2$=0.8533). The results of this study indicate that there is no evidence for development of resistance to mandipropamid in this population of P. capsici isolates collected in Korea.

• Korean Journal of Environmental Agriculture
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• v.31 no.1
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• pp.30-36
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• 2012

BACKGROUND: The resistance of rice bakanae disease pathogens against the fungicide prochloraz has been reported. Understanding the resistance mechanisms is an important for better control of the pathogens. In the present study, we investigated the resistance mechanisms of Fusarium fujikuroi CF337 (CF337) against prochloraz. METHODS AND RESULTS: Morphological changes in the cell wall of CF337 grown in potato dextrose broth (PDB) with or without prochloraz was investigated by transmission electron microscopy. Growth inhibition of CF337 was examined in PDB containing prochloraz or an ABC transporter inhibitor or both of them. Cell wall thickness of CF337 grown in PDB with prochloraz was significantly increased from $80.73{\pm}1.99nm$ to $193.11{\pm}7.07nm$. Significant inhibition in the growth of CF337 was observed in the presence of both prochloraz and the inhibitor, but no growth inhibition was observed in the presence of the inhibitor or prochloraz. Sequence analysis of ATP-binding cassette transporter (ABC) gene of CF337 showed 70 to 80% similarities to the genes of the pathogens resistant to other fungicides. CONCLUSION: Efflux transporter system and changes in cell wall thickness were suggested as resistance mechanisms of CF337 against prochloraz.