title: Identification of the G143A mutation associated with QoI resistance in Cercospora beticola field isolates from Michigan, United States.
abstract: BACKGROUND
  Cercospora leaf spot (CLS), caused by the fungus Cercospora beticola, is the most serious foliar disease of sugar beet (Beta vulgaris L.) worldwide. Disease control is mainly achieved by timely fungicide applications. In 2011, CLS control failures were reported in spite of application of quinone outside inhibitor (QoI) fungicide in several counties in Michigan, United States. The purpose of this study was to confirm the resistant phenotype and identify the molecular basis for QoI resistance of Michigan C. beticola isolates.
  
  
  RESULTS
  Isolates collected in Michigan in 1998 and 1999 that had no previous exposure to the QoI fungicides trifloxystrobin or pyraclostrobin exhibited QoI EC(50) values of ≤ 0.006 µg mL(-1) . In contrast, all isolates obtained in 2011 exhibited EC(50) values of > 0.92 µg mL(-1) to both fungicides and harbored a mutation in cytochrome b (cytb) that led to an amino acid exchange from glycine to alanine at position 143 (G143A) compared with baseline QoI-sensitive isolates. Microsatellite analysis of the isolates suggested that QoI resistance emerged independently in multiple genotypic backgrounds at multiple locations. A real-time PCR assay utilizing dual-labeled fluorogenic probes was developed to detect and differentiate QoI-resistant isolates harboring the G143A mutation from sensitive isolates.
  
  
  CONCLUSIONS
  The G143A mutation in cytb is associated with QoI resistance in C. beticola. Accurate monitoring of this mutation will be essential for fungicide resistance management in this pathosystem.
authors: Northern Crop Science Laboratory, USDA-Agricultural Research Service, Fargo, ND 58102-2765, USA. Melvin.Bolton@ars.usda.gov
authors: Melvin D
authors: MD
authors: Bolton
authors: Viviana
authors: V
authors: Rivera
authors: Gary
authors: G
authors: Secor
mesh_terms: D000085:Acetates / Q000494:pharmacology; D001203:Ascomycota / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification; D027461:Beta vulgaris / Q000382:microbiology; D002219:Carbamates / Q000494:pharmacology; D045303:Cytochromes b / Q000235:genetics* / Q000378:metabolism; D025141:Drug Resistance, Fungal / Q000187:drug effects*; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D005659:Fungicides, Industrial / Q000494:pharmacology*; D007097:Imines / Q000494:pharmacology; D008689:Methacrylates / Q000494:pharmacology; D008824:Michigan; D018895:Microsatellite Repeats; D010935:Plant Diseases / Q000382:microbiology*; D017354:Point Mutation / Q000187:drug effects*; D011720:Pyrazoles / Q000494:pharmacology; D060888:Real-Time Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D000073739:Strobilurins
chemical_list: D000085:Acetates; D002219:Carbamates; D005656:Fungal Proteins; D005659:Fungicides, Industrial; D007097:Imines; D008689:Methacrylates; D011720:Pyrazoles; D000073739:Strobilurins; D045303:Cytochromes b; C513428:pyrachlostrobin; C467051:trifloxystrobin