Non‐target site SDHI resistance is present as standing genetic variation in field populations of Zymoseptoria tritici

Abstract

BACKGROUNDA new generation of more active succinate dehydrogenase (Sdh) inhibitors (SDHIs) is currently widely used to control Septoria leaf blotch in northwest Europe. Detailed studies were conducted on Zymoseptoria tritici field isolates with reduced sensitivity to fluopyram and isofetamid; SDHIs which have only just or not been introduced for cereal disease control, respectively.RESULTSStrong cross‐resistance between fluopyram and isofetamid, but not with other SDHIs, was confirmed through sensitivity tests using laboratory mutants and field isolates with and without Sdh mutations. The sensitivity profiles of most field isolates resistant to fluopyram and isofetamid were very similar to a lab mutant carrying SdhC‐A84V, but no alterations were found in SdhB, C and D. Inhibition of mitochondrial Sdh enzyme activity and control efficacy in planta for those isolates was severely impaired by fluopyram and isofetamid, but not by bixafen. Isolates with similar phenotypes were not only detected in northwest Europe but also in New Zealand before the widely use of SDHIs.CONCLUSIONThis is the first report of SDHI‐specific non‐target site resistance in Z. tritici. Monitoring studies show that this resistance mechanism is present and can be selected from standing genetic variation in field populations. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Resistance risk assessment for Fusarium graminearum to pydiflumetofen, a new succinate dehydrogenase inhibitor

“…In the current study, four UV mutants were obtained and no mutations in any of the four Sdh genes were detected compared with their parent isolates. The absence of sdh genes mutation has been reported in other fungi . Scalliet et al .…”

“…The absence of sdh genes mutation has been reported in other fungi. 29,32,33 Scalliet et al obtained 452 SDHI-resistant mutants of Z. tritici using a UV mutagenesis approach. The absence of sdh genes mutation was observed in eight mutants (1.8%).…”

“…31 In 2017, six isolates of Z. tritici that were resistant to fluopyram and isofetamid, and had no mutations on four Sdh genes and no upregulated MgMFS1 were also detected in the field. 32 This indicated that another resistance mechanism is present and can be selected from existing genetic variation in field populations.…”

Metyltetraprole, a novel putative complex III inhibitor, targets known QoI‐resistant strains of Zymoseptoria tritici and Pyrenophora teres

“…For example, some newer SDHIs (ex. fluopyram and isofetamid) were reported to show no cross‐resistance with boscalid, an older SDHI fungicide, on some isolates with specific mutation . QoI is also one of the most important classes of fungicides owing to its broad spectrum and effectiveness in disease control.…”

“…Resistance management can be achieved by identifying molecules with a novel mode of action (MoA) or by novel adoption of molecules from a known MoA group and previously never used in cereals or by modification of molecules not affected by cross‐resistance to existing analogs. The third approach could be achieved by adjusting chemical structures of molecules to improve interaction with mutated‐target sites …”