CRYOPRESERVATION OF CULTIVATED AND WILD POTATO VARIETIES BY DROPLET VITRIFICATION PROCEDURE

The applicability to a broad range of genotypes of the selected cryopreservation procedure is one of the key issues for implementing cryopreservation in the genebank context. We tried to identify the critical factors causing differences in survival of cryopreserved shoot tips using as models one cultivated variety and one wild potato species, which were submitted to a droplet vitrification procedure, i.e., a combination of droplet-cryopreservation and vitrification. The subculture duration of the mother plants and the location of the shoot tips on the in vitro plantlets had a significant (P < 0.0001) effect on survival of cryopreserved shoot tips in both varieties. The optimal subculture duration was 7 and 5 weeks for var. Dejima (cultivated) and STN13 (wild species), respectively. The highest survival of cryopreserved shoot tips (91.9% for var. Dejima and 86.4% for STN13) was obtained after successive preculture with 0.3 M sucrose for 8 hours and with 0.7 M sucrose for 17-18 hours, dehydration with PVS2 vitrification solution (30% glycerol + 15% dimethyl sulfoxide + 15% ethylene glycol in Murashige and Skoog medium with 0.4 M sucrose) for 20 min, cooling in droplets of vitrification solution placed on aluminum foil strips and rapid warming by direct dipping of the strips in preheated unloading solution. This protocol was tested with 12 selected cultivated varieties and wild species and the survival percentages obtained ranged between 64.0 and 94.4%. It is currently being applied to Korean potato collections for the implementation of germplasm cryopreservation with minor modifications in the subculture step, i.e., subculture duration.