Flexible filamentous shallot virus X (ShVX) particles were detected in extracts of Beta vulgaris protoplasts inoculated with transcripts from a full-length ShVX cDNA. Extracts from ShVX-infected protoplast were infectious for ShVX-healthy shallot seedlings. Western blot analysis of inoculated plants revealed the accumulation of the ShVX coat protein, while electron microscopy confirmed the presence of ShVX virions. The results suggest that the in vitro RNA transcripts from full-length ShVX cDNA give rise to infectious viral particles.