Effects of light-dark cycles on the circadian conidiation rhythm in Neurospora crassa

The effects of 24 hr light-dark cycles on the circadian conidiation rhythm in Neurospora crassa were compared among wild-type frq(+) and clock mutants frq(1), frq(3), frq(7), frq(9) and frq(11). The minimum length of the light period necessary for complete entrainment to the light-dark cycles was almost 2 hr in frq(+), frq(3) and frq(7) strains. The minimum duration of the dark period necessary for the appearance of circadian conidiation was almost 4 hr in all of the strains except the frq(11) strain. The phase of the conidiation rhythm was dependent on the light to dark transition in the frq(1) strain in all light-dark cycles examined and in the frq(+) and fro(3) strains when the light period was shorter than 16 hr. In contrast, the phase of the frq(7) strain was dependent on the light to dark transition when the light period was shorter than 10 hr.