The effect of succinate dehydrogenase inhibitor/azole mixtures on selection of Zymoseptoria tritici isolates with reduced sensitivity.
BACKGROUND
Combining fungicides with different modes of action is regarded as one of the most effective means of slowing the selection of resistance. Field trials were used to study the effects of such mixtures on selection for Zymoseptoria tritici with reduced sensitivity to the succinate dehydrogenase inhibitors (SDHIs) and azole fungicides. The SDHI isopyrazam and the azole epoxiconazole were applied individually as solo products, and together in a preformulated mixture. All fungicide treatments were included at both full and half the recommended doses.


RESULTS
Compared with using epoxiconazole alone, mixing epoxiconazole with isopyrazam led to an increase in epoxiconazole-sensitive isolates. In contrast, all treatments containing isopyrazam reduced the sensitivity of Z. tritici to isopyrazam compared with those without. Reducing doses to half the recommended rate had no effect on sensitivity of isolates to either active ingredient. In a subgroup of isolates least sensitive to isopyrazam, non-synonymous mutations were found in the SdhC and SdhD subunits, but their presence was unrelated to sensitivity.


CONCLUSIONS
Mixing an azole and SDHI was clearly beneficial for the azole, but not for the SDHI component. This dynamic might change if strains conferring reduced sensitivity to the SDHIs were to arise. © 2015 Society of Chemical Industry.
Department of Crop Science, TEAGASC Crops, Environment and Land Use Programme, Carlow, Republic of Ireland.|School of Agriculture, Policy and Development, University of Reading, Reading, Berks, UK.
Hilda
H
Dooley
School of Agriculture, Policy and Development, University of Reading, Reading, Berks, UK.
Michael W
MW
Shaw
Department of Crop Science, TEAGASC Crops, Environment and Land Use Programme, Carlow, Republic of Ireland.
John
J
Spink
Department of Crop Science, TEAGASC Crops, Environment and Land Use Programme, Carlow, Republic of Ireland.
Steven
S
Kildea
D000935:Antifungal Agents; D001203:Ascomycota / Q000187:drug effects*; D001393:Azoles; D000069601:Crop Protection / Q000379:methods; D025141:Drug Resistance, Fungal; D004852:Epoxy Compounds / Q000494:pharmacology; D009636:Norbornanes / Q000494:pharmacology; D010935:Plant Diseases / Q000517:prevention & control; D011720:Pyrazoles / Q000494:pharmacology; D013385:Succinate Dehydrogenase / Q000037:antagonists & inhibitors*; D014230:Triazoles / Q000494:pharmacology; D014908:Triticum / Q000382:microbiology*
C558633:3-(difluoromethyl)-1-methyl-N-(1,2,3,4-tetrahydro-9-isopropyl-1,4-methanonaphthalen-5-yl)pyrazole-4-carboxamide; D000935:Antifungal Agents; D001393:Azoles; D004852:Epoxy Compounds; D009636:Norbornanes; D011720:Pyrazoles; D014230:Triazoles; D013385:Succinate Dehydrogenase; C109476:epoxiconazole
Fungicide; Mycosphaerella graminicola; Septoria; resistance; succinate dehydrogenase inhibitor