Bayberry twig blight caused by the ascomycete fungusPestalotiopsis versicoloris a devastating disease threatening worldwide bayberry production. However, the molecular basis underlying the pathogenesis ofP. versicoloris largely unknown. Here, we identified and functionally characterized the MAP kinase PvMk1 inP. versicolorthrough genetic and cellular biochemical approaches. Our analysis reveals a central role of PvMk1 in regulatingP. versicolorvirulence on bayberry. We demonstrate that PvMk1 is involved in hyphal development, conidiation, melanin biosynthesis, and cell wall stress responses. Notably, PvMk1 regulatesP. versicolorautophagy and is essential for hyphal growth under nitrogen-depleting conditions. These findings suggest the multifaceted role of PvMk1 in regulatingP. versicolordevelopment and virulence. More remarkably, this evidence of virulence-involved cellular processes regulated by PvMk1 has paved a fundamental way for further understanding the impact ofP. versicolorpathogenesis on bayberry.