Characterization and Genetic Analysis of a Newly Isolated Colonial Mutant of \u3cem\u3eNeurospora crassa\u3c/em\u3e

A new colonial mutant of the fungus Neurospora crassa, SS-499, was isolated by Brown (1983) following UV irradiation of wild type 74A conidia. The mutant is pale yellow in color and exhibits restricted growth with tufts of aerial hyphae unlike the spreading mycelium of the wild type strain. The mutant also produces multiple elevated growth rings, orzonations. When grown at an elevated temperature (37 C), the mutant spreads across the surface like the wild type strain with an absence of the growth ring pattern observed at the lower temperature. Microscopy revealed that the mutant has a smaller hyphal diameter than the wild type strain and produced more hyphal tips at the growing front than wild type. The mutant also produced fewer conidia than the wild type strain. The mutant also exhibited osmotic sensitivity. Because the mutant, SS-499, differed from each of the other colonials to which it was compared, a new class of colonial mutants was proposed: colonial temperature-remedial (trc). Genetic analysis of SS-499 indicated 1:1 Mendelian segregation of mutant and wild type progeny. Crosses of the mutant to tester strains located the mutant to the right of un-16 (~1% recombination) in the left arm of Linkage Group I and showed non-allelism to smco-5. Failure of SS-499 and ta to complement suggested possible allelism between the two strains