Tifluzamide shows distinct action among Rhizoctonia groups

Binucleated isolates of Rhizoctonia AG-Bb showed 28,4 times lower sensitivity to tifluzamide compared to Rhizoctonia solani AG1-IA. The result indicates intrinsic differences in the response of anastomosis groups to succinate dehydrogenase inhibitor fungicides, known as SDHI (doi 10.1002/ps.71153).

The median effective concentration, or EC50, reached 1,99 milligrams per liter in the AG-Bb isolates. In AG1-IA, the average value was 0,07 milligrams per liter.

The researchers combined sensitivity assays, structural modeling, molecular docking, molecular dynamics simulations, enzyme activity measurements, and transcriptome analysis.

Modeling indicated that tifluzamide bound to the ubiquinone pocket, formed by the SDHB, SDHC, and SDHD subunits of the succinate dehydrogenase complex. Simulations showed a stronger and more stable interaction at AG1-IA.

The binding free energy reached -36,12 kilocalories per mole in AG1-IA. In the AG-Bb group, the result was -25,76 kilocalories per mole. Tifluzamide also caused greater suppression of succinate dehydrogenase enzyme activity in AG1-IA.

Transcriptomic analysis identified specific enrichment of genes linked to the ABC transporter pathway in AG-Bb. The result suggests a greater efflux capacity, a mechanism capable of reducing the concentration of the fungicide inside the cell.

The data help explain differences in sensitivity to SDHI among Rhizoctonia groups and may support risk assessments of resistance to this class of fungicides.