Use of oxathiapiprolin for controlling soybean root rot caused by Phytophthora sojae: efficacy and mechanism of action

Background Oxathiapiprolin is a new isoxazoline fungicide developed by DuPont to control oomycete diseases. Although oxathiapiprolin has shown strong inhibitory activity against oomycete pathogens, little is known about its ability to control Phytophthora sojae. Results Oxathiapiprolin showed high inhibitory activity against Phytophthora sojae, with 50% effective concentration (EC50) values ranging from 1.15 × 10−4 to 4.43 × 10−3 μg mL−1. Oxathiapiprolin inhibited various stages of Phytophthora sojae development, including mycelial growth, sporangium formation, oospore production, and zoospore release. Electron microscopy studies revealed that oxathiapiprolin caused severe morphological and ultrastructural damage to Phytophthora sojae. Oxathiapiprolin affected the cell membrane and wall of Phytophthora sojae, making it more sensitive to osmotic and cell wall stress. Oxathiapiprolin exhibited translocation activity; it was absorbed by soybean roots and then translocated to the leaves. It was effective at reducing soybean Phytophthora root rot under glasshouse and field conditions. Both fungicide seed treatment and foliar spray significantly reduced disease incidence and yield losses compared with untreated controls in the field. Conclusion Oxathiapiprolin exhibits high inhibitory activity against Phytophthora sojae, and has multiple mechanisms of action including severe mycelial damage and modulation of osmotic and cell wall stress. These results indicate that oxathiapiprolin can be used at low concentrations for highly effective management of soybean Phytophthora root rot caused by Phytophthora sojae. © 2022 Society of Chemical Industry. Oxathiapiprolin exhibits highly effective management of soybean Phytophthora root rot caused by Phytophthora sojae, and has multiple mechanisms of action including severe mycelial damage and modulation of osmotic and cell wall stress.