Baseline and Temporal Changes in Sensitivity of Zymoseptoria tritici Isolates to Benzovindiflupyr in Oregon, U.S.A., and Cross-Sensitivity to Other SDHI Fungicides

Abstract

Zymoseptoria tritici is the causal agent of septoria tritici blotch (STB), a disease of wheat (Triticum aestivum) that results in significant yield loss worldwide. Z. tritici’s life cycle, reproductive system, effective population size, and gene flow put it at high likelihood of developing fungicide resistance. Succinate dehydrogenase inhibitor (SDHI) fungicides (FRAC code 7) were not widely used to control STB in the Willamette Valley until 2016. Field isolates of Z. tritici collected in the Willamette Valley at dates spanning the introduction of SDHI (2015-2017) were screened for sensitivity to four SDHI active ingredients: benzovindiflupyr, penthiopyrad, fluxapyroxad, and fluindapyr. Fungicide sensitivity changes were determined by EC50 values, or the fungicide concentration at which fungal growth is decreased by 50%. The benzovidiflupyr EC50 values increased significantly, indicating a reduction in sensitivity, following the adoption of SDHI fungicides in Oregon (p < 0.0001). Additionally, significant reduction in cross-sensitivity among SDHI active ingredients was also observed with a moderate and significant relationship between penthiopyrad and benzovindiflupyr (p = 0.0002), and a weak relationship between penthiopyrad and fluxapyroxad (p = 0.0482). No change in cross-sensitivity was observed with fluindapyr, which has not yet been labeled in the region. The results document a decrease in SDHI sensitivity in Z. tritici isolates following the introduction of the active ingredients to the Willamette Valley. The reduction in cross-sensitivity observed between SDHI active ingredients highlights the notion that careful consideration is required to manage fungicide resistance and suggests that within-group rotation is insufficient for resistance management.

Preventing multiple resistance above all: New insights for managing fungal adaptation

“…This situation mirrors findings previously obtained with the same approach concerning the emergence of resistance in a naïve population (Ballu et al, 2023). Several studies have documented the poor efficacy of sequences of fungicides with the same MoA for controlling target‐site resistance in Z. tritici , in the field or models (Dooley, Shaw, Spink, & Kildea, 2016; Hagerty et al, 2021; Heick, Justesen, & Jørgensen, 2017; Hobbelen et al, 2013; Mavroeidi & Shaw, 2006). Indeed, AIs with the same MoA generally display positive cross‐resistance, as confirmed by the phenotyping of our ancestral isolates.…”

Green Leaf Volatile Trans-2-Hexenal Inhibits the Growth of Fusarium graminearum by Inducing Membrane Damage, ROS Accumulation, and Cell Dysfunction

“…For example, succinate dehydrogenase inhibitor (SDHI) fungicides were effective against fungi but not oomycetes, while carboxylic acid amide (CAA) fungicides were the opposite. 52,53 Certainly, the high bioactivity and broad spectrum of T2H still need to be rigorously tested in field trials before marketing. Plant VOCs are well known for their water insolubility as lipophilic small molecular compounds.…”

“…Many existing commercial fungicides are registered only against diseases caused by fungi or oomycetes. For example, succinate dehydrogenase inhibitor (SDHI) fungicides were effective against fungi but not oomycetes, while carboxylic acid amide (CAA) fungicides were the opposite. , Certainly, the high bioactivity and broad spectrum of T2H still need to be rigorously tested in field trials before marketing.…”

Preventing multiple resistance above all: new insights for managing fungal adaptation

“…This situation mirrors findings previously obtained with the same approach concerning the emergence of resistance in a naïve population (Ballu et al ., 2022). Several studies have documented the poor efficacy of sequences of fungicides with the same MoA for controlling target-site resistance in Z. tritici , in the field or in models (Mavroeidi & Shaw, 2006; Hobbelen et al ., 2013; Dooley, H. et al ., 2016; Heick, Thies Marten et al ., 2017; Hagerty et al ., 2021). Indeed, AIs with the same MoA display positive crossresistance, as confirmed by the phenotyping of our ancestral isolates.…”