Dwarfing caused by viral pathogens and leaf malformations in ‘Shine Muscat’ grapevine

‘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 °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.