Characterization of the molecular mechanisms of resistance against DMI fungicides in Cercospora beticola populations from the Czech Republic

Authors: KUMAR, RAM - Czech University Of Life Sciences Prague; MAZAKOVA, JANA - Czech University Of Life Sciences Prague; ALI, ASAD - Czech University Of Life Sciences Prague; SUR, VISHMA PRATAP - Academy Of Science Of Czech Republic; SEN, MADHAB KUMAR - Czech University Of Life Sciences Prague; Bolton, Melvin; MANASOVA, MARIE - Czech University Of Life Sciences Prague; RYSANEK, PAVEL - Czech University Of Life Sciences Prague; ZOUHAR, MILOSLAV - Czech University Of Life Sciences Prague

Submitted to: The Journal of Fungi
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2021
Publication Date: 12/11/2021
Citation: Kumar, R., Mazakova, J., Ali, A., Sur, V., Sen, M., Bolton, M.D., Manasova, M., Rysanek, P., Zouhar, M. 2021. Characterization of the molecular mechanisms of resistance against DMI fungicides in Cercospora beticola populations from the Czech Republic. The Journal of Fungi. 7(12). Article e1062. https://doi.org/10.3390/jof7121062.
DOI: https://doi.org/10.3390/jof7121062

Interpretive Summary: Sugar beet is an important source of sucrose grown in temperate regions throughout the world including the Czech Republic. The most important disease of sugar beet in the Czech Republic is Cercospora leaf spot, which is caused by a fungal pathogen called Cercospora. Growers have traditionally been able to manage Cercospora with the application of fungicides. However, strains of Cercospora that are resistant to an important class of fungicides called the triazoles have become more common in the Czech Republic. In this research, we studied fungicide-resistant strains of Cercospora from the Czech Republic and identified a common molecular mechanism that likely explains resistance to the triazole fungicides. The identification of a genetic mutation responsible for resistance will be useful to growers in the Czech Republic and other regions where Cercospora leaf spot is problematic because it can be used to identify fungicide-resistant strains of the fungus. This will avoid the use of inefficacious fungicides, which will save farmers money.

Technical Abstract: Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is the most important foliar pathogen of sugar beet worldwide. Extensive reliance on fungicides to manage CLS has resulted in the evolution of fungicide resistance in C. beticola worldwide, including populations in the Czech Republic. One important class of fungicides used to manage CLS is the sterol demethylation inhibitors (DMI). The aim of our study was to assess DMI resistance in C. beticola from the Czech Republic and elucidate the molecular basis of DMI resistance in this population. A total of 50 isolates were collected in 2018 and 2019 from the major sugar beet growing regions of the Czech Republic and assessed for in vitro sensitivity to the DMI fungicides propiconazole, prochloraz, and epoxiconazole. These analyses identified three strains that exhibited 50% effective concentration (EC50) values > 1.0 µg mL–1 against respective fungicides, which were therefore considered resistant. In contrast, strains that exhibited lowest EC50 values were considered sensitive. To explore the molecular basis of resistance in these three strains, the cytochrome P450-dependent sterol 14a-demethylase (Cyp51) gene was sequenced. Sequence analysis identified a Y464S mutation in all three resistant strains. To assess whether Cyp51 gene expression may play a role in DMI resistance, selected strains were grown in vitro with and without fungicide treatment. These analyses indicated that Cyp51 gene expression was significantly induced after fungicide treatment. Thus, we conclude that Y464S point mutation along with induced Cyp51 gene overexpression is likely responsible for resistance against DMI fungicides in C. beticola from the Czech Republic.