conservation of Andean landraces at the International Potato Center (CIP). Ana Panta , Bart Panis , Cecilia Ynouye , Bram Criel , Rony Swennen , William Roca , a Laboratory of Tropical Crop Improvement, Katholic University of Leuven, 3001 Leuven, Belgium; b Genetic Resources Conservation and Characterization Division, International Potato Center, 12 Lima, Peru; c Laboratory of Proteomics, Centre de Recherche Public ’’Gabriel Lippmann’’, L-4422 Belvaux, Luxembourg The International Potato Center (CIP), Lima, Peru, conserves the world’s largest collection of potato genetic resources in vitro (4,421 cultivars belonging to 8 species). The development of new more efficient cryopreservation methods was urgently needed because the existing protocols were developed for only a very limit number of genotypes or species and were not applicable to the wide range diversity of Andean potato cultivars. Our experimental setup was based on reported relationships between cryopreservation and drought tolerance. Therefore, 4 cultivars showing different drought responses were selected for testing (Ccompis, Desiree, Pinaza and Wila Yari). A procedure originally designed for cryopreserving banana (Panis et al., 2005) was modified for potato apical shoot tips. It uses 2–3 mm shoot tips from 3 weeks old plantlets, 15–20 min exposure to a loading solution (LS), PVS2 treatment at 0–4 C, and ultra-rapid freezing in plastic straws (3 mm diameter · 2.5 cm length). After storage in liquid nitrogen, samples were thawed in MS salts enriched with 1.2 M sucrose and kept for 20 min. Shoot tips were cultivated on meristem medium (MS salts, 0.04 mg/l kinetin, 0.1 mg/l gibberelic acid) and 0.3–0.1 M sucrose concentrations, lowering the sucrose 0.1 M per day. Survival and recovery was evaluated 45 days after thawing. The efficiency of this protocol was compared with the method originally applied at CIP (Steponkus et al., 1992). For this, shoot-tips were exposed to different vitrifying solutions (Steponkus and PVS2) for 0, 10, 20, 30, 40, 50, 60, and 70 min. Exposure of 40–60 min to PVS2 showed the post-thaw highest recovery. Then, two methods to obtain ultra-rapid freezing and thawing rates were compared, i.e., loading in (1) plastic straw and (2) on aluminium foil strips. Post-thaw recovery rates were genotype dependent, varying from 47% for Desiree to 8% for Wila Yari, but independent of the freezing method. Finally, the effect of cold and sucrose pretreatments on the cryoability was evaluated. Plantlets were cultured during 3 weeks at 6 and 22 C in media containing 0.3 or 0.07 M sucrose. We observed that in the case of potato, a cold treatment increases the postthaw recovery rate for all four cultivars under investigation while a sugar treatment had no or even a negative effect. Analyses are now taking place to correlate the response towards cryopreservation with drought tolerance. Based on the results described in this report, CIP is currently applying the PVS2 droplet vitrification protocol routinely. As such, 150 accessions are now safely cryopreserved for the long-term. (Conflict of interest: None declared. Source of funding: None declared.)