Abstract
In the Czech Republic, demethylation inhibitors (DMIs) are used both as fungicides in controlling phoma stem canker and as growth regulators. This heavy use can result in the development of resistant isolates. A total of 45 and 286 Leptosphaeria maculans isolates were tested in vitro, using the mycelial growth and microtiter plate assays, respectively. The objective was to determine the sensitivity of L. maculans isolates collected in the Czech Republic to the fungicides tetraconazole, metconazole, and prochloraz. The mean EC50 values with the mycelial growth plate method were 1.33, 0.78, and 0.40 µg mL−1 for tetraconazole, metconazole, and prochloraz, respectively. The mean EC50 values for the microtiter plate assay were 3.01, 0.44, and 0.19 µg mL−1 for tetraconazole, metconazole, and prochloraz, respectively. All three fungicides also had high variation factors that may be due to inserts in the ERG11 promoter region. In addition, cross sensitivity among the three fungicides was observed. Overall, the high variation factors and the PCR (polymerase chain reaction) results observed in this study could signify the presence of resistant isolates in L. maculans Czech populations, especially in isolates tested for sensitivity to tetraconazole.
Highlights
Since their introduction into the agricultural fungicide market in the 1970s, demethylation inhibitor (DMI) fungicides (Fungicide Resistance Action Committee (FRAC) group 3)have been a highly effective and inexpensive way of controlling a broad range of fungi [1].They target the cytochrome P450 enzyme 14-α-demethylase, which is essential for converting lanosterol to ergosterol encoded by the ERG11 gene
DMIs are categorized as medium-risk fungicides by FRAC
Our current study showed that when tested for mycelial growth inhibition, L. maculans isolates had variation factors of 20.04, 28.83, and 73 for tetraconazole, metconazole, and prochloraz isolates, respectively
Summary
Have been a highly effective and inexpensive way of controlling a broad range of fungi [1]. They target the cytochrome P450 enzyme 14-α-demethylase, which is essential for converting lanosterol to ergosterol encoded by the ERG11 ( known as CYP51) gene. In the Czech Republic, oilseed rape cultivation accounts for about 15% of the total arable area, making it the second-most frequently grown crop [4]. Phoma stem canker ( termed blackleg disease) has become a major limiting factor in oilseed rape production [5]. Phoma stem canker is caused by the dothideomycete fungi Leptosphaeria maculans (Desm.) Ces. (anamorph Phoma lingam (Tode) Desm.) [6] and Leptosphaeria biglobosa Phoma stem canker is caused by the dothideomycete fungi Leptosphaeria maculans (Desm.) Ces. & De Not. (anamorph Phoma lingam (Tode) Desm.) [6] and Leptosphaeria biglobosa
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