First report of G143A strobilurin resistance in Cercospora beticola in sugar beet (Beta vulgaris) in Poland

Abstract

Cercospora leaf spot (CLS) caused by the fungus Cercospora beticola is the most common and destructive disease of sugar beet in Poland. Strobilurin (Quinone outside inhibitors—QoI) fungicides are widely used for CLS control. In Poland for several years, a gradual increase in QoI tolerance has been observed. In 2015, most of the tested isolates (56%) collected from several independent locations were able to grow in a PDA medium supplemented with 1 µg/ml of azoxystrobin. An additional test showed that the EC50 value for the most resistant isolates was ≥100 µg/ml, while for the sensitive ones it was ≤0.01 µg/ml. The results of cytochrome b partial DNA sequencing revealed that all resistant isolates contained single guanine to cytosine substitution (G/C), predicting the conversion of glycine to alanine at the 143 codon position (G143A). To our knowledge, this is the first report in a peer-reviewed paper on G143A mutation determining the strobilurin resistance of C. beticola in Poland.