Comparison of vitrification and encapsulation-dehydration for cryopreservation of Thymus moroderi shoot tips

Vitrification and encapsulation-dehydration were tested for cryopreservation of Thymus moroderi Pau ex Martínez (Labiatae), an endemic plant from south-eastern Spain. For vitrification, shoot tips were loaded in a solution containing 0.4 M sucrose + 2 M glycerol for 20 min at room temperature, dehydrated in PVS2 solution for 0-105 min at 0 degree C, then immersed in liquid nitrogen (LN) for at least 1 day and rapidly rewarmed. The highest survival (71.4 percent) was obtained after 60 min PVS2 dehydration. Encapsulation-dehydration gave slightly lower results, with up to 50 percent explants survival. In the optimal protocol, donor plants were cold-hardened at 10 degree C for 5 weeks, excised shoot tips precultured for 48 h on MS medium with 0.08 M sucrose, encapsulated, pretreated in medium with 0.75 M sucrose for 19 h, desiccated to 22 percent moisture content (fresh weight basis), and immersed in LN. Vitrification thus appears more suitable than encapsulation-dehydration for cryopreservation of T. moroderi shoot tips.