Baseline Sensitivity of QoI-resistant Isolates of Pyrenophora Tritici-Repentis from Argentina to Fenpicoxamid

Tan spot (TS) of wheat caused by Pyrenophora tritici-repentis (Ptr) is an important disease worldwide. Premixes of quinone outside inhibitors (QoI) and demethylation inhibitors are the most frequently used fungicides for TS control in Argentina. Recently, QoI resistance was reported in Ptr populations in Argentina, where the prevalence and intensity of this disease has increased steadily over the past decades. Therefore, development of new tools and active ingredients (a.i.) for the management of this pathosystem are needed. Fenpicoxamid is a new fungicide that belongs to the quinone inside inhibitors. This a.i. shows no cross-resistance and strong efficacy against Zymoseptoria tritici strains resistant to other fungicide classes. Here we evaluated a total of 50 QoI-resistant Ptr isolates from Argentina for their sensitivity to fenpicoxamid. Different concentrations were tested in both in vitro (0, 0.01, 0.025, 0.05, 0.075, 0.1 and 1 μg/ml) and in vivo (0, 5, 10 and 20 μg/ml) bioassays. Fenpicoxamid strongly inhibited in vitro spore germination of all tested isolates (EC50 values ranged from 0.004 to 0.067 μg/ml). In greenhouse tests, fenpicoxamid significantly decreased TS leaf incidence at 10 ppm and the average spots per leaf at 20 ppm. For the first time, we report the high fungitoxicity and lack of cross-resistance of fenpicoxamid against QoI-resistant Ptr isolates. This is a promising new a.i. for controlling TS of wheat.