Cryopreservation of white mulberry (Morus alba L.) by encapsulation-dehydration and vitrification

Shoot apices of in vitro-grown plantlets of white mulberry, Morus alba L. cv Florio, were cryopreserved using either encapsulation-dehydration or vitrification. For encapsulation-dehydration, alginate beads containing apices were dehydrated for 1, 3, 5 or 7 days in a liquid medium containing various sucrose concentrations (0.5, 0.75, 1.0 or 1.25 M). Bead desiccation was performed using silica gel for either 0, 4, 6, 8, 9 or 14 h. For vitrification, apices were directly immersed for either 5, 15, 30 or 60 min in a vitrification solution (PVS2). Following encapsulation-dehydration, treatment of alginate beads with 0.75 M sucrose was more effective in promoting regrowth of explants after immersion in liquid nitrogen than in the presence of 0.5 M sucrose for either 1 or 3 days. Regrowth of explants was also observed following vitrification and this reached 47% with increasing duration of the PVS2 treatment from 5 to 30 min. Overall, the highest frequency of explant re-growth was obtained when explants were subjected to encapsulation-dehydration in the presence of 0.75 M along with a 3 day sucrose dehydration pre-treatment and followed by desiccation for 9 h in silica gel.