Inhibitory activities of SDHI fungicides against Fusarium oxysporum f. sp. lycopersici and biological role of FoSDHC1

Fusarium wilt (FW), caused by Fusarium oxysporum f. sp. lycopersici (Fol), is one of most devastating diseases in tomato crops. None of 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 Fol were determined in vitro and the results showed that pydiflumetofen and cyclobutrifluram exhibited excellent inhibitory activities, with inhibition rates of 75.63%~87.25% at a concentration of 1 µg mL-1. Bixafen, fluopyram, isopyrazam and benzovindiflupyr exhibited weak inhibitory activities, with inhibition rates of 45.68%~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 13.45%~61.73% at a concentration of 50 µg mL-1. Forty pydiflumetofen-resistant (PR) mutants of Fol were obtained and the point mutation of FoSDHC1 was associated with resistance of Fol to pydiflumetofen. Three FoSDHC1 deletion mutants were obtained and FoSDHC1 deletion mutants exhibited no significant differences in vegetative growth, conidiation production and virulence but exhibited increased sensitivities toward all SDHI fungicides tested except thifluzamide and boscalid compared to the wild-type strain. These results indicated that FoSDHC1 regulated the sensitivity of Fol to most SDHI fungicides.