First Report of Resistance to QoI Fungicides in North American Populations of Zymoseptoria tritici, Causal Agent of Septoria Tritici Blotch of Wheat

The G143A mutation in cytb (cytochrome b gene) is associated with high levels of resistance to quinone outside inhibitor (QoI or strobilurin) fungicides that disrupt electron transport during cellular respiration (1). The G143A mutation in Zymoseptoria tritici (synonyms: Mycosphaerella graminicola and Septoria tritici), the causal agent of septoria tritici blotch of wheat (Triticum aestivum), was first reported in Europe in 2001 (1). Although Z. tritici has a global distribution (3), G143A mutants of Z. tritici have not been reported outside of Europe. We used PCR-RFLP (4) to estimate the frequencies of G143A mutants in Z. tritici populations at two locations in the Willamette Valley of western Oregon: the Hyslop Crop Science Field Research Laboratory (Hyslop Farm, HF), Benton County (44°37′52.85″ N, 123°11′55.19″ W) and research plots planted in a commercial wheat field in Washington County (45°33′58.53″ N, 123°00′11.78″ W) (North Valley Farm, NVF). Isolates originated from flag leaf collections from two...