Resistance mechanism of Fusarium fujikuroi to phenamacril in the field

BACKGROUND Rice bakanae disease mainly caused by Fusarium fujikuroi is an important disease of rice. Phenamacril has been used for controlling the disease for a few years in China. In 2016, nine phenamacril-resistant strains were found in the field of Zhejiang Province. The aim of the study was to clarify the resistance mechanism of F. fujikuroi to phenamacril and the fitness of resistant strains. RESULT The nine F. fujikuroi strains were highly resistant to phenamacril. Eight of them had the point mutation TCA (Ser)→CCA (Pro) at codon 219 in Myosin-5 protein while the other one had the point mutation TCA (Ser)→TTA (Leu) at codon 219. Myosin-5 replacement between resistant and sensitive strains confirmed that the point mutation in Myosin-5 caused the resistance of F. fujikuroi to phenamacril. Docking of phenamacril into the modeled binding pocket of Myosin-5 showed that the affinity between phenamacril and Myosin-5 decreased and hydrogen bond could not be formed between phenamacril and the amino acid at codon 219 after it changed to Pro or Leu. There was no cross-resistance between phenamacril and other fungicides. Eight resistant strains containing the point mutation S219P had almost the same fitness as the sensitive strains while the one resistant strain containing the point mutation S219L decreased mycelial growth, sporulation and pathogenicity. CONCLUSION In the field, point mutation S219P or S219L in Myosin-5 conferred high resistance to phenamacril in F. fujikuroi. The point mutation S219P did not affect the fitness of F. fujikuroi while the point mutation S219L decreased the fitness.