Cryopreservation of in vitro shoot tips of potato by droplet vitrification and genetic stability of regenerated plantlets.

Shoot tips from axillary buds of in vitro potato(Solanum tuberosum L.)were successfully cryopreserved by droplet vitrification.The optimum cryopreservation procedures were as follows.Shoot tips excised from 2–3 month-old plantlets were precultured on liquid MS medium supplemented with 0.3 mol · L-1 and 0.5 mol · L-1 sucrose for 1 day each and then dehydrated with PVS2 for 30 min at 0 ℃.Five shoot tips were transferred to approximately 15 μL droplets of PVS2 solution on thin strips of sterile aluminum foil.The aluminum foil strips were folded to enclose the shoot tips.The foil envelope was then carefully immersed into liquid nitrogen(LN)using fine forceps.After immersion the strips were quickly transferred to 2 mL cryotubes and immediately plunged into LN and maintained for 1 h at least.The shoot tips in the foil strips were then rapidly heated by immersion twice at 15 min intervals into 10 mL 1.2 mol · L-1 sucrose MS medium at room temperature.The shoot tips were then unloaded from the foil, rinsing the PVS2 from the shoot tips.The shoot tips were transferred to solid culture medium(MS + 0.5 mg · L-1 Zeatin + 0.1 mg · L-1 NAA + 1.0 mg · L-1 GA3)for recovery and regeneration.The average survival rate and regeneration rate were 79.91% and 62.52%,respectively.There was no genetic variation in the regenerated plants based on assessment of SSR markers.