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POSTERS: Fungicide and antibiotic resistance

Investigating fungicide sensitivity shifts in North American Zymoseptoria tritici field populations
Guilherme Augusti - Rothamsted Research. Bart Fraaije- Rothamsted Research, Nichola Hawkins- Rothamsted Research, Mikaela Breunig- Michigan State University, Christina Hagerty- Oregon State University, Michael Shaw- University of Reading

The fungal pathogen Zymoseptoria tritici causes worldwide Septoria tritici blotch (STB) in wheat. Under high disease pressure, control of STB is heavily dependent on foliar sprays, and, consequently, resistance shifts have been reported to different classes of fungicides (i.e. MBC, QoI, DMI and SDHI). The fungicide sensitivity status of two North American populations, sampled in Oregon and Michigan, were assessed and compared to South American, New Zealand and European field populations. Sequence analysis of CYP51, the azole target protein sterol 14?-demethylase encoding gene, indicates that resistance is evolving independently in the North American populations in comparison to European populations, albeit much slower, whereas European isolates appear to have migrated to South America and New Zealand. The Oregon and Michigan populations showed a similar sensitivity range for the SDHI bixafen. However, there were differences in fluopyram sensitivity with 61% of the Oregon strains and only 2% of Michigan strains having EC50 values >1 ppm. No mutations were found in SdhB, C and D, indicating the presence of a non-target site resistance mechanism. QoI resistance due to cytochrome b G143A is present in 68% of the Oregon strains, whereas 25% of the Michigan population is insensitive to azoxystrobin. No MBC resistant isolates were found within the Michigan population, while 22% of Oregon isolates are insensitive to carbendazim and carried beta-tubulin E198A.