'Shine Muscat' grapevines occasionally develop leaf malformations with chlorosis, vein clearing, and dwarfing. Grapevine fabavirus, grapevine geminivirus A, hop stunt viroid, and grapevine yellow speckle viroid 1 were detected in all six mother vines examined using next-generation sequencing and reverse transcription-polymerase chain reaction analyses, but 5 of 15 mother vine progenitors had no detectable viral pathogens. At 24 degrees C, leaf malformations were severe, and even clones of viral pathogen-negative vines had leaf malformations; the causes remain unclear. Infection with viral pathogens via graft inoculation from the mother vine caused severe dwarfing and severe leaf malformations.