Cryopreservation of apices of in vitro plantlets of almond (Prunus dulcis Mill.)

Apices of in vitro plantlets of almond rootstock M51 were cryopreserved usi ng the vitrification and encapsulation-dehydration techniques. With vitrifi cation, limited survival only (up to 10%) was achieved with apices which ha d been sampled on mother-plants cold-hardened at 5 degrees C for 5 weeks an d treated with the PVS2 vitrification solution for 120-180 min at O degrees C before freezing. The highest survival rates (50-62%) were achieved using encapsulation-dehydration. Optimal conditions included pregrowth of encaps ulated apices for 1 to 3 d in liquid medium with 0.75M sucrose, desiccation of beads to 19-20.3% moisture content (fresh weight basis) followed by dir ect immersion in liquid nitrogen. Comparable survival rates were obtained w ith apices of the almond cultivars Ferragnes using encapsulation-dehydratio n.