Sensitivity of Italian Zymoseptoria tritici isolates to azoxystrobin and pyraclostrobin

Zymoseptoria tritici is the causal agent of Septoria tritici blotch. The pathogen causes every year heavy yield losses in North Central Europe1 while in Italy only during the last few years, the incidence of the disease has been increased. The application of fungicides is the most widespread strategy to control this disease in particular the application of DMIs, SDHIs and multisites. Since resistance to QoIs is widespread in Europe2,3 this family has not been more recommended for control the disease4 in many regions, while in Italy QoIs can still contibute into a spray program. The aim of this study was to test the sensitivity of Z. tritici strains to QoIs in order to obtain the first information about the Italian scenario. Italian Z. tritici populations were collected during 2016-2017 from commercial, experimental and abandoned fields. Monoconidial isolates were tested for the sensitivity to azoxystrobin and pyraclostrobin and were then analyzed by Sanger sequencing for the presence of G143A substitution. By droplets digital PCR, the allele frequency in the populations were established. Results highlighted the widespread presence of G143A substitution in experimental fields. These results showed the emergence of resistance to QoI in Italian Z. tritici populations, mainly in experimental fields where less stringent anti-resistance strategies were applied. This highlight the importance of sound anti-resistance strategies listed at FRAC web page http://www.frac.info/working-group/qol-fungicides/general-use-recommendations, in commercial fields.