Cryopreservation of apple (Malus x domestica Borkh.) shoot tips following encapsulation-dehydration or encapsulation-vitrification

Axillary shoot tips of apple cv. Golden Delicious isolated from shoot cultu res were successfully cryopreserved using the encapsulation-de hydration te chnique. After encapsulation in alginate gel, embedded shoot tips were dehy drated by exposure to a sterile air flow before being frozen in liquid nitr ogen and subsequent slow thawing. A preculture on modified MS medium contai ning 0.75 M sucrose followed by 6 h of dehydration (21% residual water) led to the highest shoot regrowth of frozen, coated shoot lips (83.7%). Among the sugars tested, sucrose and sorbitol presented the best cryoprotective e ffect. Four other scion apple varieties and rootstocks were also successful ly cryopreserved. Axillary shoot lips of five apple (Malus x domestica Bork h.) scion and root-stock cultivars were cryopreserved using the encapsulati on-vitrification technique. Using a one-step freezing method, we successful ly cryopreserved axillary shoot tips without the requirement of a cold hard ening pretreatment of the shoot cultures. Cryopreserved shoot tips treated with aqueous cryoprotective mixture IV containing 180% (w/v) sucrose and 12 0% (v/v) ethylene glycol showed the highest shoot regrowth rates, which var ied from 64% to 77%, depending on the cultivar.