Highly Conserved Allelic Substitutions S202F, L244P, and H248P/R/Y in FsSdhB and A83 V in FsSdhC1 Trigger Gradual Resistance to Pydiflumetofen in Fusarium solani.

Pydiflumetofen (Pyd), one of the new-generation SDHIs, has been applied to control various diseases in economic crops. Fusarium solani, a soil-borne pathogen with a broad host range, is the agent of quinoa basal-stem rot (QBSR). In this study, three PydLR (4.64 < RF < 9.31), six PydMR (51.24 < RF < 86.91), and seven PydHR mutants (RF > 6000) were generated by Pyd-taming. Most F. solani PydR mutants showed no fitness penalties. The sequence alignment of FsSdh genes revealed that substitutions S202F, L244P, and H248P/R/Y in FsSdhB, or A83 V in FsSdhC1, caused Pyd resistance. Notably, the mutation S202F causing HR was first reported. Molecular docking demonstrated that these aforementioned mutations significantly reduced affinity between Pyd and the Qp-binding pocket. These results provide pivotal data for the resistance management strategies of F. solani and advance our understanding of the resistance mechanisms of SDHIs.