Cryopreservation of apple in vitro shoot tips by the droplet freezing method

Shoot tips sampled on in vitro plantlets of 5 apple cultivars were successf ully cryopreserved using the droplet freezing method. After 3 weeks of cold -hardening at 5 degrees C, the shoot tips were precultured in liquid medium with 1.0% DMSO for 24 h at 5 degrees C, treated for 75 min. at room temper ature with 0.3 M sucrose and 15% DMSO, placed in 5 mu l droplets of cryopro tectant medium containing 0.3 M sucrose and 15% DMSO on aluminium foil and cooled to -40 degrees C at 0.2 degrees C/min before immersion in liquid nit rogen. Recovery rates of cryopreserved shoot tips ranged between 70 and 92% , depending on the cultivar. Regrowth of frozen shoot tips was direct, with out callus formation.