title: Metrafenone resistance in a population of Erysiphe necator in northern Italy.
abstract: BACKGROUND
  Metrafenone has been used in Europe in integrated pest management programmes since 2006 to control powdery mildews, including Erysiphe necator. Its exact mode of action is not known, but it is unique among fungicide classes used in powdery mildew management. Recently, resistance to metrafenone was reported in Blumeria graminis f. sp. tritici. In this study we investigated metrafenone resistance in Erysiphe necator in northern Italy.
  
  
  RESULTS
  Metrafenone efficacy to control grapevine powdery mildew was monitored in three consecutive years in the field, and its reduced activity was observed in 2013. Out of 13 monoconidial isolates, two sensitive strains were identified, which did not grow at the fungicide concentration recommended for field application. The remaining strains showed variable response to metrafenone, and five of them grew and sporulated similarly to the control, even at 1250 mg L(-1) of metrafenone. Moreover, the resistant strains showed cross-resistance to pyriofenone, which belongs to the same FRAC group as metrafenone.
  
  
  CONCLUSIONS
  The results indicate the emergence of metrafenone resistance in an Italian population of Erysiphe necator. Further studies are needed to gain insight into the metrafenone's mode of action and to understand the impact of resistance on changes in the pathogen population structure, fitness and spread of resistant strains, which will be indicative for designing appropriate antiresistance measures.
authors.affiliation: Department of Food, Environmental and Nutritional Sciences, University of Milan, Milan, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Kunova
authors.affiliation: Department of Food, Environmental and Nutritional Sciences, University of Milan, Milan, Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Pizzatti
authors.affiliation: Department of Food, Environmental and Nutritional Sciences, University of Milan, Milan, Italy.
authors.forename: Maria
authors.initials: M
authors.lastname: Bonaldi
authors.affiliation: Department of Food, Environmental and Nutritional Sciences, University of Milan, Milan, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Cortesi
mesh_terms: D001203:Ascomycota / Q000187:drug effects*; D001577:Benzophenones / Q000494:pharmacology*; D025141:Drug Resistance, Fungal; D005638:Fruit / Q000382:microbiology; D005659:Fungicides, Industrial / Q000494:pharmacology*; D007558:Italy; D010935:Plant Diseases / Q000382:microbiology / Q000517:prevention & control*; D018515:Plant Leaves / Q000382:microbiology; D027843:Vitis / Q000382:microbiology*
chemical_list: D001577:Benzophenones; D005659:Fungicides, Industrial; C511340:metrafenone
keywords: Oidium tuckeri; Uncinula necator; Vitis vinifera; benzophenone; fungicide resistance; pyriofenone