Cryopreservation of ulluco ( Ullucus tuberosus Cal.) and oca ( Oxalis tuberosa Mol.) shoot tips using the PVS2 droplet-vitrification method.

摘要

Ulluco (Ullucus tuberosus Cal.) and oca (Oxalis tuberosa Mol.) are Andean tuber crops of significant importance for the nutrition and subsistence of the Andean people. The world's largest germplasm collections of these crops, comprised of 544 and 628 accessions of ulluco and oca, respectively, are maintained at the International Potato Center (CIP). For their long-term conservation, CIP is currently developing cryopreservation techniques. Post-thaw survival and recovery resulting from shoot cryopreservation using plants cultured under different temperature regimes were investigated with 4 accessions each of ulluco and oca. Apical shoot tips from 3-week-old in vitro ulluco and oca plantlets were cryopreserved using the droplet-vitrification protocol. Shoot tips of 2 mm size were exposed to a loading solution for 20 min, dehydrated with PVS2 for 0, 15, 30, 45, 60 and 75 min, at 0 degrees C, transferred to aluminium foil strips and plunged into liquid nitrogen. The highest recovery after cryopreservation was 35 and 15% for ulluco and oca, respectively, using 60 min of exposure to PVS2. In a second assay, in vitro donor plants of ulluco and oca were cultured at a constant temperature of 6 degrees C, or alternating temperatures of 18 degrees C in week 1 and 6 degrees C in week 2. Shoot tips were cryopreserved following the protocol described above with 60 min exposition of exposure to PVS2. A constant low temperature did not increase the recovery percentage after cryopreservation. It did increase, however, with 5% in ulluco and 4% in oca plantlets when alternating temperatures were applied. These results showed that cryopreservation could be applied for long-term conservation of ulluco and oca germplasm collections.