In the case of wild type, it is usually preferable to test 3-4 day old colonies before conidiophores are formed. Age-1 mutant colonies do not form conidiophores. Mutant and wild type colonies as old as 10 days can be used, but wild type conidiophores must be removed with a forcible stream of water because they obscure the reactions. The solution is shielded from light because the dye slowly photo-oxidizes. Overnight incubation increases the overall intensity, but does not increase the differential.
Mutant colonies are intensely blue to purple, but wild type is colorless or faintly blue.
Microscopically, large blue formazan granules occur on the surface of mutant colonies, whereas the faint stain of wild type is diffuse within hyphae. Thus, the secretion phenotype is a general feature of the mutants. We do not know whether the high spontaneous frequency of the mutants is a feature of other wild types, but one should be aware of the phenomenon in wild type control tests. The superoxide test has been successfully applied to colonies derived from random ascospores in crosses of mutant to wild type or the linkage testers multicent and alcoy in analysis of segregation and recombination. 3108 from the Department of Genetics.