Efficient elimination of virus complex from garlic (Allium sativum L.) by cryotherapy of shoot tips

Vegetative propagation of plants, such as garlic (Allium sativum L.), is known to facilitate the transmission of several virus species throughout the plant cycles. This process favors the onset of complex diseases by accumulation of different species in the same plant, resulting in decreased productivity and production quality. Studies have reported the use of cryotherapy of shoot tips, or meristematic clusters, as an efficient tool for obtaining virus-free plants. This study aimed to evaluate the ability of cryotherapy to eradicate virus complex in garlic plants. Bulbils naturally infected with Onion Yellow Dwarf Virus (OYDV), Leek Yellow Strip Virus (LYSV) and Garlic Common Latent Virus (GCLV) were employed as explants for different virus-cleaning treatments tested. Dot-ELISA and RT-PCR analysis were used to demonstrate the presence/absence of virus complex, and histological analysis was also performed to confirm these results. Five days after cryotherapy, structural analysis revealed that cooling had caused cell damage, as indicated by the increased vacuolization of cells after cryotherapy, as well as slight plasmolysis after thermotherapy. Immunolocalization analysis indicated the subcellular distribution of OYDV in garlic shoot tips in association with the development of plasmodesmata, while no OYDV was detected in the first cell layers of the meristematic dome. Cryotherapy successfully removed virus complex, resulting in virus-free plants with enhanced efficiency, compared to conventional meristem culture-based techniques. Moreover, the synergistic effects of cryotherapy and thermotherapy resulted in a 40 % survival rate of shoot tips and the regeneration of 90, 100 and 80 % OYDV-, LYSV- and GCLV-free plants, respectively.