Development of a PVS2 Droplet Vitrification Method for Potato Cryopreservation

BACKGROUND: CIP maintains the largest in vitro clonal potato collection in the world, comprising 4,013 landraces and 3,353 improved accessions. The in vitro technology is more efficient and secure than conservation in the field, allowing in vitro plantlets to be stored for approximately 2 years without sub-culture. This method however is not ideal for the long-term germplasm conservation because it is labor consuming, costly, and carries risks of losing accessions due to human error, such as contamination and mislabeling during sub-culturing. OBJECTIVE: To improve the potato cryopreservation procedure based on the droplet PVS2 vitrification. METHODS: The improved method is as follows: excision of 1.8-2.5 mm apical shoot tips from 3 weeks old cultures; 15 min exposure to a loading solution and 50 min to PVS2 (at 0°C); ultra-rapid cooling on aluminum foil strips (0.5 x 2 cm) in LN; rewarming (20 min) in 1.2 M sucrose MS liquid medium; post-cryo culture in the dark on potato meristem medium with progressively decreased sucrose levels (daily transfers from 0.3, to 0.2, to 0.1 M and maintained on 0.07 M). This method was compared with those previously applied by IPK (Germany) and CIP potato genebanks. RESULTS: Survival and recovery were higher using the PVS2 droplet method. Cultivars from several species, one frost tolerant ( Solanum juzecpzukii, cv. Piñaza) and two drought tolerant (S. tuberosum subsp andigena, cv Ccompis, and Solanum spp, cv Desiree) responded similarly. CONCLUSIONS: The improved method is recommended for the long term conservation of diverse potato germplasm.