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.