Genetic mechanism, baseline sensitivity and risk of resistance to oxathiapiprolin in oomycetes

• Published in: Pest management science 2022-03, Vol.78 (3), p.905-913
• Main Authors: Mboup, Mamadou Kane, Sweigard, James W, Carroll, Anne, Jaworska, Grazyna, Genet, Jean‐Luc
• Format: Article
• Language: English
• Subjects: Agricultural sciences; Airborne microorganisms; Amino acids; Commercialization; Downy mildew; fungicide resistance; Fungicides; Fungicides, Industrial - pharmacology; Hydrocarbons, Fluorinated; Irradiation; Late blight; Late blight fungus; Low concentrations; Mutagenesis; Oomycetes - genetics; OSBP; oxathiapiprolin; Phytophthora capsici; Phytophthora infestans; Phytophthora infestans - genetics; Plant Diseases; Plasmopara viticola; Product development; Pyrazoles; Resistant mutant; Risk; Sensitivity; Ultraviolet radiation
• ISSN: 1526-498X; 1526-4998
• DOI: 10.1002/ps.6700

BACKGROUND Oxathiapiprolin is a piperidinyl thiazole isoxazoline fungicide discovered by DuPont and commercialized by Corteva Agriscience. It acts by inhibiting a novel fungal target, an oxysterol binding protein (OSBP), and is intrinsically highly active against oomycetes including grape downy mildew (Plasmopara viticola) and potato late blight (Phytophthora infestans). Because the fungicide acts at a single site there is a need to determine the risk of resistance development. RESULTS Oxathiapiprolin controlled European Plasmopara viticola and Phytophthora infestans isolates at very low concentrations with half maximal effective concentration (EC50) values ranging from 0.001 to 0.0264 mg L−1 and 0.001 to 0.03 mg L−1, respectively. Laboratory mutagenesis studies performed with Phytophthora capsici using ultraviolet (UV) irradiation generated mutants with reduced sensitivity to oxathiapiprolin. All resistant mutants had a base pair change in the OSBP gene that resulted in an amino acid change. Most common substitutions were S768Y, G770V, G839W and L863W. Isolates of Plasmopara viticola and Phytophthora infestans with reduced sensitivity were also detected in field trial sites where oxathiapiprolin had been applied repeatedly each season over several consecutive years. CONCLUSIONS The risk of oxathiapiprolin resistance development in Plasmopara viticola and Phytophthora infestans is medium to high and strict resistance management measures are required. Over‐exposure of target populations to single‐site fungicides during product development should be avoided. Oxathiapiprolin is a new oomycete fungicide. Laboratory mutagenesis studies produced Phytophthora capsici mutants with reduced sensitivity to oxathiapiprolin. Plasmopara viticola and Phytophthora infestans field samples from development trials with season‐long applications of the fungicide showed reduced sensitivity to oxathiapiprolin. The resistance risk associated is moderate to high and requires management. © 2021 Society of Chemical Industry.