Induction and Characterization of Penicillium caseicolum Mutants Resistant to Ergosterol Biosynthesis Inhibitors.

The isolation of Penicillium caseicolum mutants resistant to different fungicides which inhibit ergosterol biosynthesis is reported. Mutational frequencies for resistance were high (3 x 10 to 3 x 10). The levels of resistance toward the inhibitors of sterol C-14 demethylation were always low (<10), whereas high values were obtained with mutants resistant to inhibitors of sterol Delta14 reduction or Delta8-->Delta7 isomerization, or both. Generally, there was a positive cross-resistance between fungicides showing the same biochemical mode of action but not between compounds of two different groups. Mycelial growth rate and sporulation were tested; several mutants were not affected for these characteristics. We conclude that resistance to ergosterol biosynthesis inhibitors may be used as a good marker for genetic studies through protoplast fusion.