Fludioxonil Resistance in <i>Fusarium fujikuroi</i> : Biological Characteristics and Resistance Mechanisms

Rice bakanae disease (RBD), caused by <i>Fusarium fujikuroi</i>, threatens global rice production. While the phenylpyrrole fungicide fludioxonil shows efficacy against <i>F</i>. <i>fujikuroi</i>, resistance mechanisms remain understudied. The current study found that the fludioxonil sensitivity of 101 <i>F</i>. <i>fujikuroi</i> isolates collected in the rice fields of Xinxiang City in the Henan Province of China ranged from 0.025 to 0.759 μg/ml, with an average EC₅₀ value of 0.3441 ± 0.1961 μg/ml (standard error). Four highly fludioxonil-resistant <i>F</i>. <i>fujikuroi</i> laboratory mutants were generated by repeated exposure to fludioxonil, and they exhibited enhanced mycelial growth and sporulation but reduced spore germination, pathogenicity, and osmotic stress tolerance, alongside abnormal hyphae. Molecular analysis identified amino acid substitutions in the target protein Ffos-1, notably at residue 672 (A672P/T). These acid amino changes reduced the minimum binding energy in docking models. <i>Ffos-1</i> expression was significantly (<i>P</i> < 0.05) upregulated in fludioxonil-resistant <i>F</i>. <i>fujikuroi</i> mutants. Meanwhile, cross-resistance analysis revealed a significant (<i>P</i> = 0.0064) correlation between fludioxonil and iprodione but not epoxiconazole, prothioconazole, or carbendazim. However, field monitoring is critical, as baseline shifts could compromise fludioxonil efficacy. These findings highlight Ffos-1's role in fludioxonil action and resistance, informing integrated strategies to delay resistance spread and improve RBD management.