Cryopreservation of Malus cultivars: Comparison of two droplet protocols

Two droplet procedures, droplet-vitrification (PVS2) and droplet (DMSO) were applied for cryopreservation of in vitro cultured apple (Malus domestica Borkh., cvs. Florina, Idared, Colmar and Rebra) plants. The highest post-thaw regrowth rates (70% for cv. Florina, 66% for cv. Idared, 63% for cv. Colmar and 60% for cv. Rebra) were achieved after using the droplet-vitrification (PVS2) protocol. The excised shoot tips (2–3 mm in length) were precultured in 0.5 M sucrose enriched media for 24 h. Subsequently they were transferred in PVS2 vitrification solution for 30 or 40 min (depending on cultivar) at 24 °C and then immersed in liquid nitrogen. Rewarming was performed in liquid MS medium at 24 °C. Plants regenerated from cryopreserved shoot tips did not display any sign of morphological alteration or abnormalities in growth in comparison with control plants.