Characterization, Genetic Analysis and Reversion of a Fungicide-Resistant Mutant of \u3cem\u3eNeurospora crassa\u3c/em\u3e

One problem associated with the use of chemicals to control fungal pathogens in crops is the development of fungicide-resistant organisms. Studies of mutants which are resistant to fungicides may lead to an understanding of the mechanism(s) by which the mutant acquired resistance. These types of studies may also elucidate the mode of action of the fungicide and lead to the development of more effective fungicides. Mutants of the genetically well-known, but non-pathogenic fungus, Neurospora crassa, offer an ideal system in which to study fungicide resistance. A mutant, KT-27, resistant to the dicarboximide fungicide vinclozolin, had been isolated in the Georgia Southern Neurospora Genetics Laboratory and had been found to be osmotic-sensitive. Furthermore, the osmotic-sensitivity co-segregated with vinclozolin resistance. Complementation tests and a cross of KT-27 to os-1 supported allelism of the two mutants. In KT-27, rate of hyphal elongation, amount of biomass, time preceding conidial germination and percent conidial germination, for KT-27 were more adversely affected by the presence of vinclozolin in the medium than they were in the wild type 74 strain. On media with and without vinclozolin, the vinclozolin-resistant KT-27 was found to have decreased sporulation in comparison to wild type. Revertant isolates were generated to examine the forward mutation, and six of these were analyzed. A comparison of the rates of hyphal elongation and biomass and germination of conidia on media with and without vinclozolin identified three revertants which were no longer osmotic-sensitive and no longer vinclozolin-resistant. Three partial revertants that were no longer osmotic-sensitive, but which continued to be vinclozolin-resistant were also identified. Genetic analysis was indicative of five of the revertants having a genetic basis of reversion. Genetic analysis of one was characteristic of the presence of a modifier. These results indicate that osmotic sensitivity and vinclozolin resistance may be under the control of different portions of the product of the os-1 locus