A new point mutation (E198T) in β-tubulin confers resistance to carbendazim in Fusarium incarnatum.

Carbendazim is commonly used to control maize stalk rot caused by Fusarium species, and its resistance mainly arises from point mutations in the amino acids of β-tubulin. In this study, we identified two field isolates of Fusarium incarnatum resistant to carbendazim. One moderately resistant isolate, HA16R (100 μg/mL > MIC>50 μg/mL) carried a β-tubulin F167Y point mutation, while the other highly resistant isolate, HA18R (MIC >100 μg/mL) harbored a novel β-tubulin substitution at position 198-E198T. Fitness assessment revealed that HA18R exhibited reductions in both mycelial growth and spore germination. Cross-resistance tests showed a positive cross-resistance with thiabendazole, but the isolates remained sensitive to tebuconazole, prochloraz, pyraclostrobin, and fludioxonil. Site-directed mutagenesis experiments demonstrated that the E198T mutation in β-tubulin confers high-level resistance to carbendazim. Additionally, the resistance levels conferred by different amino acid substitutions at position 198 (E198L, E198K, and E198Q) were also compared. Molecular docking analysis further revealed that the variation in resistance levels among these mutations is associated with distinct binding modes between carbendazim and β-tubulin. In conclusion, this study is the first to report a novel substitution at position 198 in the β-tubulin of Fusarium incarnatum-E198T, which confers high-level resistance to carbendazim, and it also reveals the differences in resistance levels caused by different point mutations (E198K, E198L, and E198Q). These findings provide new molecular insights into the field resistance mechanism of carbendazim and offer valuable information for the management of maize stalk rot.