Cryopreservation of in vitro shoot apices of Oxalis tuberosa Mol.

Oca (Oxalis tuberosa Mol.) is an under-utilized tuber crop from the Andean region. Cryopreservation would allow the safe and long-term preservation of the genetic resources of this crop. A protocol for the cryopreservation of in vitro grown shoots has been developed using the vitrification solution PVS2. Two genotypes were studied (G1 and G27). Nodal segments were cultured on MS medium and incubated at 10°C with 16 h photoperiod and 10 mol m⁻² s⁻¹ irradiance, for two weeks. Apices were then excised and cultured on MS + 0.15 M sucrose for 3 days at 5°C in darkness. Subsequently, apices were immersed in a loading solution (liquid MS medium + 2 M glycerol + 0.4 M sucrose), and then treated with the vitrification solution PVS2 for 0-40 minutes. Cryovials were then immersed in liquid nitrogen. Four weeks after rewarming and culture on recovery medium, genotype G1 showed approximately 60% recovery (normal growth) with 20 min PVS2 treatment. Genotype G27 showed lower recovery (30%). Differential scanning calorimetry yielded a Tg midpoint for PSV2 solution of ca. −120°C. Calorimetric studies on apices at different stages of the cryopreservation protocol showed a change in calorimetric parameters consistent with a decrease in the amount of frozen water as the protocol advanced.