| Nitrate non-utilizing mutants(nit) were recovered from carbendazim(MBC) resistant mutants and wild type isolates of Gibberella zeae cultured on MMC media, which contains 2.5% potassium chlorate. These nit mutants could be divided into four physiological phenotypes by their growth on supplemented minimal agar medium with different nitrogen resources. These classes presumably reflect mutations at a nitrate reductase structural locus(nit),a nitrate assimilation pathway specific regulatory Iocus(nit3),Ioci (often more) that affect the assemble of a molybdenum-containing cofactor necessary for nitrate reductase activity(NitM), and locus that affect the major nitrogen regulatory(nitA). It was found that all the nit mutants were resistant to chlorate, the growth rate on PSA plate and sexual reproduction ability haven't changed as compared with their parent isolates. Although the conidial sproulation of nit mutants changed more or less both on Joff's broth and on 5% mung bean broth, but there was no correlation between the change of sporulation and nit mutation. The nit mutation could be steadily inherited by self-cross process and asexual reproduction. There was no cross resistance between chlorate and MBC in G. zeae. Therefore, the nit can be used as gnetic marker for study the genetics of MBC resisance in homothallic fungus G. zeae.According to the ability of the field isolates of G. zeae to grow on the PSA with varying MBC (MBC) concentrations, three sensitivity levels of isolates were determined in vitro. The sensitive isolates (S) could grow at 0.5μg/ml, but were completely inhibited at 1.4μg/ml. The moderate resistant isolates (MR) could grow fast at 1.4μg/ml and slow at 50μg/ml, but could not grow at 100μg/ml. The high resistant isolates (HR) could grow faster than MR at 50μg/ml, and also could grow at 100μg/ml. No low resistant isolates , which could grow at 1.4μ g/ml but could not grow at 50μg/ml, were found among the field isolates. The resistance to MBC can be steadily inherited by self-cross process or asexual reproduction. Genetic study showed that the genes for MBC resistance and nitrate assimilationon different linkage groups, and the two levels of MBC resistance in G. zeae are conferred by mutations at two sites or two mutations at one site 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.The laboratory MBC-resistant mutants of wild-type of G. zeae were generated in the laboratory by ultra-violet(UV) irradiation and fungicide selection on sub-lethal concentration . Two levels of resistance were identified (low,LR; high,HR) , the LR mutants could grow at critical dosage of 1.4μg/ml of MBC, and completely inhibited above 10μg/ml concentration, but this phenotype of isolate was not found in the field; the HR mutants could grow at 100μg/ml ,and showed negative cross-resistance with N-phenylcarbamate fungicides, such as N- (3,5- dichloro-phenyl) carbamate (MDPC), while the LR mutants were not; the MR(moderate resistant) which could grow fast at 10μg/ml and slow at 50μg/ml, but could not grow at 100μg/ml, were not generated in laboratory. The HR mutants of MR which isolated from field were also generated by fungicide selection on 100μg/ml of MBC, but these mutants didn't express negative cross-resistance to MDPC. In studied resistant mutants, the resistance to MBC can be steadily inherited by asexual reproduction and self-cross process, and most of them were pathogenic to wheat seedling. The genetics of laboratory-resistance to MBC, as well as sensitive to MDPC were investigated in different phenotype mutants. The results showed that the resistance to MBC was controlled by the same single major gene in laboratory mutants and field resistant isolates of G. zeae, and the different levels of resistance or the same resistant level in different strains maybe conferred by mutations at different sites or different mutations at one site in the same locus. Therefore, the MBC-re...
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