Characterization and Genetic Analysis of Osmotic-Sensitive Mutants of \u3cem\u3eNeurospora crassa\u3c/em\u3e

Backcrosses to wild-type N. crassa 74A were made with 17 F1 progeny of 15 osmotic-sensitive mutants isolated in the Neurospora Laboratory at GSC. The original mutants were of four types: osmotic-sensitive with wild-type morphology (Type 1), osmotic-sensitive with failure to separate conidia (Type 2), osmotic-sensitive with altered morphology (Type 3), and osmotic sensitive with altered morphology and failure to separate conidia (Type 4). A 1:1 Mendelian segregation of the traits was observed for most of the F1 progeny. Crosses showed linked but separate loci for osmotic sensitivity and altered morphology in Type 3 mutants and linked but separate loci for the three traits in all but one (SS-302) of the Type 4 mutants. Existence of Type 1 mutants and segregation of altered morphology from osmotic sensitivity in all but one of the others indicated that grossly altered morphology was not a necessary condition for osmotic sensitivity in Neurospora. No segregation of the three traits was observed in SS-302 which resembles known osmotic mutants and is linked to LG I or II but is not allelic to os-1 or os-5. Crosses of other mutants to tester strains for mapping suggested new loci for osmotic sensitivity in LG VI and for osmotic sensitivity and separation of conidia in LG IV or V. The mutant SS-499 was mapped to 13 m.u. from mating-type in LG I. SS-931 was found to be a new mutant with grossly wild-type morphology and co-segregating traits of osmotic sensitivity and separation of conidia. The mutant locus mapped to LG III and linked to ad-2 and trp-1. Some but not all of the mutants were sensitive to media containing increased concentrations of glucose instead of NaCl . Some but not all of the mutants were resistant to media containing sorbose. Two mutants were resistant to the fungicide vinclozolin. Differences in appearance and in production of conidia of osmotic-sensitive mutants and mutants being investigated were found on complete media vs. W-M media