Cryopreservation of apple shoot tips: Importance of cryopreservation technique and of conditioning of donor plants

In this gaper, the efficiency of three techniques (two-step freezing, vitri fication, encapsulation-dehydration) for freezing irt vitro shoot tips was compared and the effect of conditioning of mother-plants was investigated. Cold-hardening mother plants for 3 weeks at 5 degrees C improved regrowth r ate and pattern of shoot tips whatever the cryopreservation technique emplo yed. Increasing the time during which mother-plants were maintained on stan dard medium without subculture before sampling of apices decreased the wate r content of shoot tips from about 85-88% to 63-66% (fresh weight basis) an d increased regrowth rate and pattern whatever the cryopreservation techniq ue employed. The best results (up to 86% regrowth after cryopreservation wi thout any callusing) were obtained with the encapsulation-dehydration techn ique. Using apices sampled on mother-plants which had not been subcultured for 26 weeks allowed to reduce the duration of the sucrose pregrowth treatm ent of encapsulated apices, thus simplifying the protocol. This simplified encapsulation-dehydration protocol was successfully applied to II out of th e 12 cultivars tested.