REGENERATION IN MINT (MENTHA × PIPERITA) CRYOPRESERVED APICES: CAN THE CRYOPRESERVATION TECHNIQUE, REGENERATION MEDIUM COMPOSITION AND GENOTYPE AFFECT THE FINAL RESULT?

One of the most reliable methods for long-term conservation is cryopreservation, mainly due to its capability to guarantee the genetic stability of the preserved material. During the development of cryopreservation protocols the composition of the growth recovery medium is of vital importance in order to obtain fully viable structures without callus formation. Two cryopreservation techniques (droplet-vitrification and encapsulation-dehydration) and three different recovery media were compared with shoot apices of two mint genotypes (MEN 186 and MEN 198). The medium was supplemented with: 1) 0.5 mg/L 6-benzylaminopurine; 2) 0.5 mg/L 6-dimethylallylamino-purine + 0.1 mg/L α-naphthalene acetic acid; or 3) 0.5 mg/L 6-benzylaminopurine + 0.1 mg/L α-naphthalene acetic acid. Survival and regeneration (shoot growth) were studied after a 4-week recovery period. Although the recovery media did not influence survival in any of the two genotypes or protocols, the regeneration percentage observed was affected by the growth regulators. When the encapsulation-dehydration protocol was employed this influence was detected even in control apices (not subjected to cooling in liquid nitrogen), while with the droplet-vitrification method recovery medium had an effect only on cryopreserved apices. In all these cases, the medium without auxin (only with cytokinin) resulted in higher recovery rates, i.e., organized growth was favoured.