Molecular and transcriptomic insights into differential sensitivity of Rhizoctonia anastomosis groups to the SDHI fungicide thifluzamide.

Background

Sensitivity to succinate dehydrogenase inhibitor (SDHI) fungicides varies considerably among Rhizoctonia anastomosis groups, yet the molecular basis of this variation remains poorly understood. In this study, the mechanisms underlying the contrasting responses of multinucleate Rhizoctonia solani AG1-IA and binucleate Rhizoctonia AG-Bb to the SDHI fungicide thifluzamide were investigated through an integrated analysis combining fungicide sensitivity assays, structural modeling, molecular docking, molecular dynamics simulations, enzymatic activity measurements and transcriptome profiling.

Results

Baseline sensitivity tests revealed a pronounced difference between the two groups. The mean median effective concentration (EC50) value of AG-Bb isolates (1.99 mg L-1) was nearly 28.4-fold higher than that of AG1-IA (0.07 mg L-1), indicating markedly lower sensitivity in the binucleate strain. Structural modeling showed that thifluzamide binds to the ubiquinone-binding pocket formed by SDHB, SDHC and SDHD of the succinate dehydrogenase (SDH) complex. Molecular dynamics simulations further demonstrated a stronger and more stable interaction in AG1-IA, reflected by a substantially lower binding free energy (-36.12 kcal mol-1) compared with AG-Bb (-25.76 kcal mol-1). Consistently, thifluzamide elicited substantially stronger suppression of SDH enzymatic activity in AG1-IA than in AG-Bb. Transcriptomic analysis revealed that genes involved in the ABC transporter pathway were specifically enriched in AG-Bb, suggesting enhanced efflux capacity.

Conclusion

These findings provide mechanistic insight into intrinsic SDHI sensitivity differences among Rhizoctonia groups and contribute to resistance risk assessment for SDHI fungicides. © 2026 Society of Chemical Industry.