This research identified and characterized a virus that causes brown discoloration in commercially cultivated white mushrooms (Flammulina velutipes). The virus, named FvBV, belongs to a family of fungal viruses called Partitiviridae and is unique because it causes visible symptoms, unlike most similar viruses. The researchers developed a method to detect the virus and confirmed its direct link to mushroom browning. Impacts on everyday life: • Helps mushroom farmers identify and understand the cause of quality-reducing brown discoloration • Enables better quality control in commercial mushroom production • Contributes to maintaining the visual appeal and market value of white mushrooms • Provides tools for screening mushroom cultures for viral infection before cultivation • Aids in developing strategies to prevent economic losses in mushroom farming