Survival of in Vitro-grown Apical Meristems of Pyrus Following Cryopreservation

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Abstract
Apical meristems of four pears (Pyrus communis L. cv. Beurre Hardy, P. koehnei Schneider, P. cossonii Coss. and Dur., and a hybrid, P. dimorphophylla Makino × P. fauriei Schneider) were tested for their ability to survive immersion in liquid nitrogen. Plantlets were grown in vitro at 25C or cold-hardened for 1 week at – 1C before cooling at rates of 0.1, 0.3, 0.5, and 0.8 C/rein to –40C, followed by plunging the vials into liquid nitrogen. Vials were thawed for 1 min at 40C. A cryoprotectant mixture of polyethylene glycol, glucose, and dimethylsulfoxide (DMSO) was used. Regrowth of meristems ranged from 0% to 61% for plants grown at 25C and from 5% to 95% for cold-hardened plants. Cold-hardening significantly improved the recovery rates of all species tested. Survival rates increased as cooling rates decreased. Survival rates were not linked to the geographic origin of the species tested.