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

Shoot tips sampled on in vitro plantlets of 5 apple cultivars were successfully cryopreserved using the droplet freezing method. After 3 weeks of cold-hardening at 5°C, the shoot tips were precultured in liquid medium with 1.0% DMSO for 24 h at 5°C, treated for 75 min. at room temperature with 0.3 M sucrose and 15% DMSO, placed in 5 micrometer droplets of cryoprotectant medium containing 0.3 M sucrose and 15% DMSO on aluminium foil and cooled to -40°C at 0.2°C/min before immersion in liquid nitrogen. Recovery rates of cryopreserved shoot tips ranged between 70 and 92%, depending on the cultivar. Regrowth of frozen shoot tips was direct, without callus formation. (Résumé d'auteur