First report of strobilurin resistance in field samples of Blumeria graminis f. sp. tritici, causal agent of powdery mildew in wheat, in Paraguay

Wheat powdery mildew is caused by the fungus Blumeria graminis f.sp. tritici which can lead up to 40% of losses in the grain production. Chemical treatment with strobilurins (Quinone outside inhibitors—QoI) is widely used to control the disease. However, a point mutation in the cytochrome b gene (G143A) of the fungus can provide resistance to strobilurins-based fungicides. Five field samples of the fungus were collected from wheat infected plants, and DNA was extracted for the analysis. The bioassay indicated that all samples were resistant to the strobilurin azoxystrobin 50% (Amistar®, 500 g/kg) in in vivo tests. Molecular analysis (allele-specific PCR and sequenced amplicons) confirmed the presence of both alleles (resistant and susceptible to strobilurins) in all samples. To our knowledge, this is the first report of the presence of strobilurin resistance allele G143A in Blumeria graminis f.sp. tritici in Paraguay.