The action of high concentrations of benomyl was investigated in
the wild-type strain St Lawrence of Neurospora crassa and in
mutants displaying various levels of tolerance to the drug. Germ-tube
formation by macroconidia, germination pattern (single versus
multiple germ-tube emergence) and hyphal tip extension of these strains
showed different sensitivities to the microtubule inhibitor,
benomyl. The wild-type strain, whose vegetative growth was inhibited at
micromolar concentrations, still germinated by multipolar
outgrowth at 100 μm. At such a level, germination of the
moderately resistant mutant Bml 511(r) was inhibited more than
the wild
type. Highly resistant mutants capable of hyphal growth at
500 μm were obtained by mutating strain Bml 511(r)
using uv. One of
these, strain E1-91, showed temporary sensitivity to the microtubule
inhibitor and produced multiple germ-tubes. This strain was
deficient in the β-tubulin polypeptide during the first hour of germination.