Phenotypic Fungicide Resistance and Cross-Resistance Among Nothopassalora personata Populations

Late leaf spot, caused by Nothopassalora personata, is an economically important disease of peanut that routinely requires several applications of preventative fungicides. The objectives of this study were to quantify the risk of phenotypic fungicide resistance and potential cross-resistance among N. personata populations. A total of 59 samples of N. personata isolates were collected from 28 grower or research fields in South Carolina, Georgia, and Virginia. Phenotypic resistance of isolates was evaluated against 14 fungicides and a nontreated control, with active ingredients from the quinone outside inhibitor, demethylation inhibitor, and succinate-dehydrogenase inhibitor (SDHI) classes. Overall, visual incidence of lesion development 15% or greater 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 indicate potential N. personata populations with SDHI cross-resistance. Although 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 a multi-site mode of action in fungicide programs are advised for preserving fungicide efficacy or reducing selection pressure. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .