Cryopreservation of apple shoot tips by encapsulation-dehydration: Effect of preculture, dehydration and freezing procedure on shoot regeneration

Shoot tips sampled on in vitro cultured apple plantlets of 6 accessions of M. domestica and one accession of M. robusta were successfully cryopreserve d using the encapsulation-dehydration technique. Shoot tips were excised fr om plantlets which had been submitted to 3 weeks of cold-acclimation at 5 d egrees C, 70 d after their last subculture. After preculture at 5 degrees C in media with progressively increased sucrose concentration (0.1 M,0.3 M a nd 0.7 M), shoot tips were encapsulated and pregrown in medium with 1.0 M s ucrose for I d, dehydrated for 4 h under the air current of the laminar flo w cabinet, thus reaching a moisture content of around 30% (fresh weight bas is) and directly immersed in liquid nitrogen. The regeneration rate of cryo preserved apices varied between 70 and 90%, depending on the accession. Usi ng apices sampled on plantlets which had been maintained on standard medium without subculture for 6 months, sucrose preculture became unnecessary to achieve regrowth after cryopreservation and the dehydration period was shor tened. These experiments showed that the physiological state of the plant m aterial directly affects the results and procedures for cryopreservation of apple shoot tips.