Evolution of QoI resistance of the wheat pathogen Zymoseptoria tritici in Northern France

Quinone outside Inhibitors (QoIs), also referred as strobilurins, have been widely used to manage Zymoseptoria tritici, the causal agent of Septoria tritici blotch of wheat. A few studies from the last decade reported the occurrence of Qol resistance in most European countries. However, no information is today available on the current distribution of such a resistance. A total of 828 single-conidial isolates collected between 2005 and 2015 years (65 in 2005, 32 in 2009, 166 in 2011, 337 in 2012 and 228 in 2015) were used to assess the evolution of Z tritici Qol resistance in Northern France. The resistance was determined by screening the cytochrome b G143A substitution conferring QoI resistance, using a PCR-based mismatch mutation assay. The frequencies of resistant isolates increased from 83.1% in 2005 to 96.9% in 2009 and then reached almost 100% from 2009 to 2015 (100% in 2011, 99.7% in 2012 and 99.6% in 2015). Such a finding highlights a full and possibly irreversible widespread of Z. tritci Qol resistance in Northern France and indicates a lack of recent introduction of sensitive genotypes to this region from other areas, where 1 tritci Qol resistance has not emerged or is not widespread yet. Maintaining the use in the field, but in a reasoned manner, of other fungicide classes such as DMIs and SDHIs to manage Z tritici is therefore still strongly justified. (C) 2016 Elsevier Ltd. All rights reserved.