Characterization and fitness of carbendazim-resistant strains of Fusarium graminearum (wheat scab).

BACKGROUND Carbendazim (MBC) has failed to control wheat scab, caused by Fusarium graminearum Schwabe, on the eastern coast of China in recent years after about 30 years of application. RESULTS MBC resistance was found to be common in pathogen populations on the eastern coast and along areas of the Yangtze River. EC(50) and minimum inhibitive concentration (MIC) values of MBC inhibiting mycelium growth of wild-type isolates were less than 0.9 and 1.4 microg mL(-1) respectively, while EC(50) values of resistant collections averaged 7.02 +/- 11.86 microg mL(-1). The slope of the MBC dosage-response curve (DRC) for resistant isolates of F. graminearum was flat: 1 < b < 2.8 for resistant isolates and 3.5 < b < 11 for sensitive isolates). Both field resistant and sensitive MBC strains shared similar temperature sensitivity, fitness and virulence on ears. Field resistant strains and UV-induced mutants showed positive cross-resistance to other benzimidazole derivatives and were mainly at intermediate MBC resistance level. Highly resistant field MBC strains rarely appeared, but only some of the highly resistant MBC UV mutants were insensitive to N-phenylaminecarbamates. No mutation in beta-tubulin was found in F. graminearum, in contrast to mutation in this tubulin which has led to MBC resistance in other plant pathogens. CONCLUSION MBC(R) isolates have high fitness and competition in field, conferred by a novel molecular mechanism.

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