Phenotypic fungicide resistance and cross-resistance among Nothopassalora personata populations

Abstract

Late leaf spot, caused by Nothopassalora personata, is an economically important disease of peanut which routinely requires preventative fungicide application. The objectives of this study were to quantify the risk of phenotypic fungicide resistance and potential cross-resistance among Nothopassalora personata populations. A total of 59 samples of N. personata isolates were collected from 28 grower or research fields in SC, GA, and VA. Phenotypic resistance of isolates was evaluated against 14 fungicides and a nontreated control, with active ingredients from the quinone outside inhibitor (QoI), demethylation inhibitor (DMI), and succinate-dehydrogenase inhibitor (SDHI) classes. Overall, lesion development ≥ 15% was observed with nearly all isolates for at least one of the active ingredients tested. Correlations between active ingredients, penthiopyrad and pydiflumetofen, as well as bixafen plus flutriafol and pydiflumetofen, and their lesion development risk indicates potential N. personata populations with SDHI cross-resistance. While these data do not confirm the presence of genetic resistance markers, results paired with observed reduced efficacy in the field reinforce the strong need for an integrated approach in managing late leaf spot. In areas with high probabilities for resistance to several modes of action, longer rotations out of peanut, varieties with greater levels of resistance, earlier planting, and continued incorporation of active ingredients with multi-site mode of action in fungicide programs are advised for preserving fungicide efficacy or reducing selection pressure.