Novel Modifications ΔI127/L85R in FsSdhD Are Involved in Differential Resistance to Pydiflumetofen in Fusarium solani

Abstract Lentil root rot (LRR), caused by the soil-borne fungal pathogen Fusarium solani, severely threatens lentil production. Pydiflumetofen (Pyd), a succinate dehydrogenase inhibitor (SDHI) fungicide, is applied to manage diseases caused by Fusarium spp. In this study, the frequency distribution of 50% inhibitory concentration (EC50) of F. solani to Pyd was established, and the mean EC50 value was 0.089 ± 0.0080 μg/mL. A total of 12 Pyd-resistant (PydR) mutants were generated through Pyd-taming, and the resistance frequency was 0.6%. Sequence analysis identified that distinct amino acid substitutions, A85 V in FsSdhC2 or L85R, ΔI127, and D128N in FsSdhD, were associated with moderate to high levels of Pyd resistance. Molecular docking indicated that all mutations significantly reduced the binding affinity between Pyd and the FsSdh complex. These findings advance our mechanistic understanding of SDHI resistance and provide scientific directions for controlling LRR using Pyd.