Loss of nitrofuran resistance in Fusarium oxysporum is correlated with loss of a 46.7 kb circular DNA molecule

Strain FC1, a wild-type isolate of the phytopathogenic fungus Fusarium oxysporum, is resistant to nifuroxime, a nitrofuran derivative. Mutants sensitive to this compound arise at high frequency by vegetative segregation. Resistance to nifuroxime is inherited as an extranuclear marker in crosses between a nifuroxime-sensitive variant and the wild-type. Nifuroxime-sensitive strains are also unable to express an exopolygalacturonase activity present in the wild-type. For one strain tested, it was shown that the ability to parasitize a susceptible tomato plant variety was also lost. Loss of nifuroxime resistance was concomitant with the loss of a 46.7 kb circular DNA molecule.