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.