Inhibitory Effects of Garlic Extract on Hop Stunt Viroid in Micropropagated Grapevine Plantlets

Hop stunt viroid (HSVd) is a major pathogen that affects grapevine health and causes substantial economic losses in grape cultivation. Many studies have been conducted to control grapevine diseases, but effective control methods after plant infections remain lacking. This study aimed to assess the antiviral potential of garlic extract, a natural substance that inhibits HSVds in grapevine plants after micropropagation. Garlic extract was diluted 1,000-fold and applied to grapevine plants, and its effect on HSVd accumulation was evaluated using reverse transcription polymerase chain reaction and digital PCR. The results showed that HSVd accumulation was significantly reduced, with an inhibition rate of 74.45%; meanwhile, higher garlic extract concentrations resulted in contamination and plant damage. Nanopore sequencing confirmed that the integrity of the HSVd genome was compromised after treatment. Furthermore, garlic extract inhibited the HSVd and promoted plant growth by enhancing shoot and root development. Additionally, inhibition of the HSVd was sustained in regenerated grapevine plants. Moreover, the garlic extract showed inhibitory effects against HSVds in natural host cucumber plants. These results suggest that garlic extract could be a cost-effective and sustainable alternative for viroid control in grapevine cultivation, providing long-term protection and broader antiviral activity across plant species.