Resistance Risk Assessment of Propiconazole in <i>Rhizoctonia solani</i> and its Synergistic Antifungal Mechanism with Kresoxim-methyl

The resistance risk and mechanisms of propiconazole in <i>Rhizoctonia solani</i> remain unclear. In this study, the sensitivity of 159 <i>R. solani</i> isolates to propiconazole was determined, and the EC₅₀ value was 0.2286 μg/mL. Nineteen propiconazole-resistant mutants of <i>R. solani</i> were obtained through fungicide adaptation, and the compound fitness indexes of these propiconazole-resistant mutants were lower than those of their parental isolates. Cross-resistance analysis revealed that there was no cross-resistance between propiconazole and other fungicides, apart from prochloraz. Although no point mutations occurred in the <i>RsCYP51</i> gene or its promoter regions, the expression levels of <i>RsCYP51</i> and efflux transporter genes increased substantially in the propiconazole-resistant mutants. Furthermore, a 1:1 synergistic combination of propiconazole and kresoxim-methyl (SCpk(1:1)) could simultaneously cause more severe damage to both cell membrane integrity and mitochondrial function. Field trials demonstrated that SCpk(1:1) achieved over 86% control efficacy against rice sheath blight applied at 120 g a.i./ha.