Deciphering Reduced Field Sensitivity to Propiconazole and Its Molecular Mechanisms in <i>Microdochium paspali</i> Infecting <i>Paspalum vaginatum</i> Sw.

Sparse leaf patch (SLP), caused by Microdochium paspali, is a destructive disease of seashore paspalum. Propiconazole, a demethylation inhibitor fungicide, is the primary chemical used for SLP management. In this study, the sensitivity of 96 M. paspali isolates to propiconazole was assessed. Compared with sensitive isolate I16, other isolates collected from golf course exhibited reduced sensitivity to propiconazole. Three types of point mutations were detected in MpCYP51: Type I (19%): MpCYP51 T161S; Type II (6%): MpCYP51 T94I–H103F-I165T-C178G; and Type III (74%): MpCYP51 T94I–H103F-T161S–I165T-C178G . Functional validation confirmed that the T161S substitution in MpCYP51 confers reduced sensitivity to propiconazole. Additionally, induced overexpression of MpCYP51 in Type II mutation isolates represents another major mechanism underlying reduced sensitivity. Both point mutations and induced overexpression of the MpCYP51 gene were identified as key contributors to reduced sensitivity to DMI fungicides, providing a theoretical basis and technical guidance for the rational use of DMI fungicides and effective SLP management.