A major gene for resistance to carbendazim, in field isolates ofGibberella zeae

Isolates of Gibberella zeae were collected from wheat fields at two sites in China. A total of 56 isolates were characterized for their ability to grow on the potato sucrose agar amended with various concentrations of carbendazim. Three sensitivity levels were identified among the isolates tested: sensitive (S) isolates could grow at 0.5 μg·mL−1, but were completely inhibited at 1.4 μg·mL−1 ; moderately resistant (MR) isolates grew quickly at 1.4 μg·mL−1, slowly at 50 μg·mL−1, and were completely inhibited at 100 μg·mL−1 ; highly resistant (HR) isolates were slightly inhibited at 50 μg·mL−1, but only partially inhibited at 100 μg·mL−1. Six isolates representing the three sensitivity level phenotypes were randomly selected for a study on the inheritance of carbendazim resistance by analyzing the sensitivity of hybrid F1 progeny. The nitrate nonutilizing mutant (nit) was used as a genetic marker to confirm that individual perithecia were the result of out-crossing. Five cross were assessed: S × S, MR × S, MR × MR, HR × S, and HR × MR. In crosses between the parents with different sensitivity levels, i.e., MR × S, HR × S, HR × MR, the progeny fit a 1:1 segregation ratio of the two parental phenotypes. No segregation was observed in the crosses of S × S and MR × MR. We conclude that the MR and HR phenotypes in G. zeae are conferred by different allelic mutations within the same locus. In these isolates, resistance to carbendazim was not affected by modifying genes or cytoplasmic components.