Inhibitory Activities of SDHI Fungicides Against <i>Fusarium oxysporum</i> f. sp. <i>lycopersici</i> and the Biological Role of <i>FoSDHC1</i>

Fusarium wilt (FW), caused by <i>Fusarium oxysporum</i> f. sp. <i>lycopersici</i> (<i>Fol</i>), is one of the most devastating diseases in tomato crops. None of the succinate dehydrogenase inhibitor (SDHI) fungicides is registered for the control of FW of tomatoes in China. In this study, the inhibitory activities of 12 SDHI fungicides against <i>Fol</i> were determined in vitro, and the results showed that pydiflumetofen and cyclobutrifluram exhibited excellent inhibitory activities, with inhibition rates of approximately 75.63 to 87.25% at a concentration of 1 μg ml^-1. Bixafen, fluopyram, isopyrazam, and benzovindiflupyr exhibited weak inhibitory activities, with inhibition rates of approximately 45.68 to 75.00% at a concentration of 20 μg ml^-1. Penflufen, sedaxane, isofetamid, boscalid, thifluzamide, and carboxin exhibited very poor inhibitory activities, with inhibition rates of approximately 13.45 to 61.73% at a concentration of 50 μg ml^-1. Forty pydiflumetofen-resistant mutants of <i>Fol</i> were obtained, and the point mutation of <i>FoSDHC1</i> was associated with resistance of <i>Fol</i> to pydiflumetofen. Three <i>FoSDHC1</i> deletion mutants were obtained, and <i>FoSDHC1</i> deletion mutants exhibited no significant differences in vegetative growth, conidiation, and virulence but exhibited increased sensitivities toward all SDHI fungicides tested except thifluzamide and boscalid compared with the wild-type strain. These results indicated that <i>FoSDHC1</i> regulated the sensitivity of <i>Fol</i> to most SDHI fungicides.