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Characterization of a Mycovirus Associated with the Brown Discoloration of Edible Mushroom, Flammulina velutipes

Summary

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

Background

At the time mycoviruses were discovered in white button mushrooms in 1962, Lentinula edodes was the only artificially cultivated mushroom in Japan. As the mushroom industry grew, various abnormal symptoms appeared during cultivation, including spontaneous brown discoloration of white fruiting bodies in Flammulina velutipes strains. Spherical virus particles were detected in the brown discolored fruiting bodies, tentatively named FvBV (Flammulina velutipes browning virus).

Objective

To characterize and sequence the mycovirus (FvBV) previously identified in brown discolored fruiting bodies of cultivated Flammulina velutipes mushrooms, and determine its relationship to the browning phenomenon.

Results

The FvBV contained two dsRNA genomes – dsRNA1 (1,915 bp) encoding a 66-kDa RNA-dependent RNA polymerase (RdRp) and dsRNA2 (1,730 bp) encoding a 60-kDa coat protein. Phylogenetic analysis revealed FvBV to be a Partitivirus most closely related to Chondrostereum purpureum cryptic virus. RT-PCR screening found three wild isolates from central Japan contained FvBV. Fruiting bodies from FvBV-infected strains showed consistently darker brown coloration compared to virus-free strains.

Conclusion

The study established a clear association between the presence of Partitivirus FvBV and dark brown coloration of F. velutipes fruiting bodies. This appears to be unique as partitiviruses typically cause symptomless infections in fungi. The RT-PCR assay developed enabled reliable detection of FvBV and confirmation of its link to the browning phenotype.
  • Published in:Virology Journal,
  • Study Type:Laboratory Research,
  • Source: 10.1186/1743-422X-7-342
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