[Genetics of resistance to carbendazim in Gibberella zeae]

According to the ability of the field isolates of Gibberella zeae to grow on the PSA with varying carbendazim(MBC) concentrations, three sensitivity levels of isolates were determined in vitro. The sensitive isolates(S) could grow at 0.5 microgram/ml, but were completely inhibited at 1.4 micrograms/ml. The moderate resistant isolates (MR) could grow fast at 1.4 micrograms/ml and slow at 50 micrograms/ml, but could not grow at 100 micrograms/ml. The high resistant isolates(HR) could grow faster than R at 50 micrograms/ml, and also could grow at 100 micrograms/ml. No low resistant isolates, that could grow fast at 1.4 micrograms/ml but could not grow at 50 micrograms/ml, were found among the field isolates. The genetics of resistance to carbendazim in G. zeae was investigated by analyzing the sensitivity of sexual outcrossed progeny to MBC. The nitrate non-utilizing mutant (nit) as an another added genetic marker was used to select the out-crossed perithecium from self-crossed perithecia. Seven crosses were tested in all, including cross between S x S, MR x S, MR x MR, HR x S, as well as HR x MR. The results showed that no recombinant phenotype was found among all progeny of seven crosses. Progeny segregation of crosses between the parents with different sensitive levels(i.e. MR x S, HR x S, HR x MR) clearly fit a 1:1 ratio of two parental phenotypes, and no segregation was found in the crosses of S x S and MR x MR. So it can be concluded that the two levels of MBC resistance in G. zeae are conferred by two loci mutations or one locus with different allelic mutations that constitute a polymorphic series in a single Mendelian gene. In these isolates, the MBC resistance is not affected by modifying genes or cytoplasmic components.