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POSTERS: Fungicide and antibiotic resistance

Impact of CYP51 gene copy number and expression on DMI fungicide resistance in Blumeria graminis f.sp. tritici
Emily Meyers - North Carolina State University. Christina Cowger- North Carolina State University, James Brown- John Innes Centre, Corinne Arnold- John Innes Centre, Christina Cowger- USDA-ARS Plant Science Unit

Wheat powdery mildew, caused by Blumeria graminis f.sp. tritici (Bgt), is notorious for quickly becoming resistant to fungicides. Rapid adaptation to early demethylation inhibitor (DMI) fungicides was observed in European fields after intensive DMI use in the early 1980’s. These old European Bgt isolates with reduced DMI sensitivity were found to contain a Y136F mutation in CYP51, the 14?-demethylase protein targeted by DMI fungicides. Recent fungicide tests of United States (U.S.) Bgt isolates have revealed reduced DMI sensitivity in the eastern U.S., where wheat powdery mildew occurs most regularly, as compared to the Plains states. The same Y136F mutation was found in U.S. isolates, but was not highly correlated with reduced DMI sensitivity. Recently sampled DMI-resistant United Kingdom (U.K.) isolates with at least double the reduction in sensitivity were found to have multiple CYP51 gene copies and increased CYP51 gene expression. Some U.K. isolates and several U.S. isolates were found to possess both wildtype and mutant CYP51 alleles; however, the U.K. mutant alleles had a double mutation of Y136F and S509T, while U.S. mutant alleles had only the Y136F mutation. The S509T mutation was not found in U.S. isolates, indicating that S509T is specific to DMI resistance in European Bgt. To determine the underlying cause of the reduced DMI sensitivity observed in U.S. Bgt, evaluation of CYP51 gene copy number and expression in U.S. isolates is currently underway.