Circadian rhythm organizes inner physiology with respect to the external world, providing life with the ability to anticipate and thereby better prepare for major fluctuations in its environment.To determine its function in Magnaporthe oryzae, the causal agent of rice blast, we functionally characterized the MoFRQ gene that is orthologous to FRQ of Neurospora crassa.The Mofrq mutant had no obvious defect in vegetative growth but was significantly reduced in conidiation.It also was radically reduced in conidium germination and appressorium formation on hydrophobic surfaces.Deletion of MoFRQ also impacted plant infection and virulence.Invasive growth and lesion development were significantly reduced in the Mofrq mutant.The transcription level of MoFRQ was up-regulation under light conditions compared with that of in the dark.Furthermore, cAMP-dependent PKA activities were reduced in the Mofrq mutant.Our results indicate that the MoFRQ gene is important to conidiation, conidial germination, appressorium formation, and pathogenesis in M.oryzae.