A quantitative survey of conidiation mutants in Aspergillus nidulans.

A quantitative survey has been made of conidiation mutants in Aspergillus nidulans. Conidiation mutants were 6 to I 3 times more numerous than auxotrophic mutants, but growth tests showed that the mutant defect in 85 % of the conidiation mutants was not confined to conidiation. The number of loci specifically involved in conidiation was estimated to be 45 to 150. Mutants were classified according to the stage of the developmental block and also into asporogenous and oligosporogenous types; 64 % were oligosporogenous, but in further tests, 84 % of the asporogenous mutants were found to be temperature sensitive or slightly leaky, suggesting that many of the loci involved act only as modifiers in conidiation. The largest group of mutants was blocked before conidiophore formation, while many others failed at ill-defined stages of conidiation, suggesting that failure was due to the gradual build-up of metabolic deficiencies. A class of conidial maturation mutants has also been identified.