Application of vitrification-derived cryotechniques for long-term storage of poplar and aspen (Populus spp.) germplasm

The application of three different vitrification-based freezing strategies for the cryostorage of white poplar (Populus alba L.) and hybrid aspen (P. tremula L. x P. tremuloides Michx.) have been assessed. The PVS2 vitrification protocol was Successfully applied to two white poplar in vitro clones stored for more than 6 months in slow-growth conditions (4 degrees C, in darkness) and showing clear signs of explant etiolation and decay. After 60 min of PVS2 treatment, P. alba L. (cv. Villafranca) explants isolated from axillary buds demonstrated significantly better potential for post-freeze regrowth (64%) compared to those obtained from apical buds (17%). Similarly, a high level of survival (78%) of the frozen hybrid aspen shoot tips was recorded following the application of the same technique. Using the 'encapsulation-vitrification' procedure, no toxic effects of the PVS2 treatment were noticed after 120 min exposure, however none of the cryopreserved (poplar and aspen) explants survived after 3 weeks. In contrast, the 'droplet-vitrification' technique appeared to be very efficient in the cryopreservation of white poplar shoot tips, which increases the opportunities for wider application of this method in other woody species.