Selection of conidial longevity mutants of Neurospora crassa.

Conidial survival was measured after incubation in white light at 30 degrees C and 85-100% relative humidity. The heritable median lifespan (MLS) of the wild-type ( age0 ) was 22 days. Spontaneous short-lived mutants (age-) with MLS about 7 days occurred among both sexual and asexual progeny of wild-type at a frequency of about 10%. Radiation of conidia with near ultraviolet light increased the mutation frequency about 5-9-fold above spontaneous. The apparent spontaneous reversion frequency was about 0.1% or less. Four lines of evidence indicated that conditional defective conidiophorogenesis is a pleiotropic expression of the age- mutations. Of five age- mutants tested, all were photosensitive and remedial by vitamin E, exhibiting wild-type survival in darkness or after preculture with vitamin E. Selective breeding yielded variants (age+) with about 14-day increments of MLS at each of three generations beyond the F1. The segregation of either age- or age+ in crosses to age0 was Mendelian. A survey of mutants of 61 genes with other biochemical or morphological phenotypes indicated, as a conservative estimate, that 9 or 15% may exert a pleiotropic adverse effect on conidial longevity.