• Research in Plant Disease
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• v.8 no.4
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• pp.239-244
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• 2002

Among 34 isolates of Colletotrichum spp., 20 from red pepper and 14 from apple, only one isolate 2001-45 was identified as the isolate resistant to sterol biosynthesis inhibiting fungicides. EC$_{50}$ values of the isolate 2001-45 were 153.5, 42.7, 34.0, and 17.1 $\mu\textrm{g}$/ml for myclobutanil, tebuconazole, hexaconazole and nuarimol, respectively, The resistance factor of the isolate 2001-45 against the other isolate 2001-44 to 4 above fungicides was ranged from 17 to 57. However, EC$_{50}$ value of the 2001-45 for prochloraz was 0.07 $\mu\textrm{g}$/ml, which was lower than those of the 2001-44 and the isolate JC24. For the fitness test of the 2001-45, mycelial growth, sporulation on PDA and pathogenicity on fruits were investigated. No difference in mycelial growth was found between 2001-45 and 2001-44, but great difference in sporulation. No symptom was developed by 2001-45 even by wound inoculation of pepper fruit. Therefore, this study indicated that the isolate 2001-45 was inferior to the other isolates in the fitness, although the isolate 2001-45 was highly resistant to sterol biosynthesis inhibiting fungicides.

• The Korean Journal of Pesticide Science
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• v.12 no.3
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• pp.277-282
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• 2008

To assess the resistance to prochloraz, $EC_{50}$ values of Fusarium isolates obtained from rice seed were investigated through the agar dilution method. $EC_{50}$ value of 36 isolates of Fusarium spp. to prochloraz ranged from 0.020 to $1.78{\mu}g\;mL^{-1}$ with an average of $0.25{\mu}g\;mL^{-1}$. According to the species of Fusarium, the average $EC_{50}$ value was fluctuated; $0.091{\mu}g\;mL^{-1}$ for F. moniliformis, $0.11{\mu}g\;mL^{-1}$ for F. proliferatum and $0.31{\mu}g\;mL^{-1}$ for F. fujikuroi. The resistant baseline was decided at $0.5{\mu}g\;mL^{-1}$ to determine if the isolate was resistant to prochloraz or not. Based on the resistant baseline, the ratio of resistant isolates was 14%. There was no correlation between the resistance to prochloraz and the pathogenicity of Fusarium spp. on rice seedlings. The resistant isolates of F. fujikuroi did not show the cross-resistance to other sterol biosynthesis inhibiting fungicides, triflumizole, hexaconazole, difenoconazole and tebuconazole.

• The Korean Journal of Pesticide Science
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• v.7 no.3
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• pp.159-168
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• 2003

With microtiter plate, the assay method was developed for detecting the fungicidal activity of new compounds against spore germination, spore adhesion and mycelial growth of Colletotrichum sp. JC24 cal1Sing red pepper anthracnose. Also, the effects of some commercialized fungicides on fungal development like above mentioned were investigated by measuring the optical density of mycelia grown into wells of microtiter plate. For the standardization of assay method, some factors, such as the treatment of MTT and/or propanol, inodulum density and incubation period, affecting on mycelial optical density were investigated. For obtaining precise and consistent mycelial optical density, it was necessary the treatment of MTT for 12 hrs and propanol for 1 hr. inoculum density adjusted to $1\times10^5$ spores/mL and incubation period for 36 hrs at $25^{\circ}C$. For fungicidal activities, 6 protective fungicides, 6 ones inhibiting sterol biosynthesis, and one inhibiting respiration were used in this study. While mancozeb, chlorothalonil and dithianon among 6 protective fungicides inhibited strongly spore germination, adhesion, and mycelial growth at $6.25{\mu}g/mL$, propineb, iminoctadine and fluazinam inhibited intermediately spore germination and mycelial growth at $100{\mu}g/mL$. Washing above 3 fungicides with new PD broth, their activity against spore adhesion decreased. With hexaconazole, tebuconazole and myclobutanil, the tendency of the activity against fungal differentiation of the early infection stage was similar to the latter group of protective fungicides, showing the decrease of the inhibitory activity against spore adhesion by washing 2 hrs after incubation. However, kresoxim-methyl inhibited spore adhesion distinctly, depending on the applied concentrations. Based on these results, it might be able to assess the fungicidal activity of many compounds against spore germination, adhesion and mycelial growth by the use of microtiter plate in vitro. Using the assay developed in this report, it was possible to investigate the inhibitory activity of some commercialized fungicides, too.