No Evidence of QoI Resistance in Apple Powdery Mildew (Podosphaera leucotricha)

Sensitivity monitoring studies using detached leaf tests with isolates of Podosphaera leucotricha showed no adaptation to pyraclostrobin in the last years. Sequence analysis of the target gene of QoIs, cytochrome b, of different isolates of P.leucotricha showed the presence of an intron directly after codon 143. This makes the occurrence of the G143A mutation unlikely. On the other hand, intron sequences have not been detected in immediate vicinity to the codons 129 and 137; therefore, the occurrence of those two mutations cannot be excluded. As the effects of these mutations on field performance on QoI fungicides are rather low, the overall resistance risk of P.leucotricha to this fungicide class is estimated to be low. The amplified cytochrome b gene fragments (exons and introns) for samples from different European countries and Australia were highly conserved.