Cryopreservation is an effective and efficient strategy for the long-term conservation of clonally propagated crops. Plant material is stored at ultra-low temperatures in the vapor or liquid phase of liquid nitrogen (-196°C) and at this temperature physiological, chemical, and metabolic activities slow to an extremely low rate. Germplasm can theoretically remain viable for centuries.
CIP began cyroperserving potatoes in 1996 and after experimenting with a wide range of protocols and variables, the CIP genebank adopted the PVS2-droplet method, originally developed for the Musa (banana) collection. The CIP genebank has improved the protocol where to date the genebank successfully cryopreserves >450 potato accessions per year (Link to potato OP).
In 2013, strict standards for viability assessment, decision-making (thresholds on material to keep or discard), operation, health and safety, and quality control were implemented to ensure long-term fidelity of the germplasm (Link to OP) A crucial part of our standards are that cryopreserved shoot tips maintain the capacity to develop into normal looking in vitro plants with a functional apex, stem, leaves, and roots, without any intermediate callus formation, after removing them from liquid nitrogen (LN) and passing them through the post-thawing recovery steps. For protocols click here.
Per accession, the CIP genebank cryopreserves 150 shoot tips, of which 30 are thawed for baseline viability determination after a minimum of 24 hours in LN. Depending on the viability rate of the first run, one single run is carried out if the viability is ? 30%or two runs are stored (first run: viability of 20-30%, second run: viability of ? 20%). Accessions that show less than 20% viability are discarded, and will be cryopreserved again in the future with a more specific protocol.
The identity and tracking of accessions throughout the cryopreservation process si done with bidimensional barcode labels, and sample location and assessment data in real-time is determined with the use of hand-held pocket PCs and barcode printers.
Currently, CIP’s cryobank holds 1,450 potato accessions with an average shoot tip recovery (viability) rate of 56%. Routine cryopreservation of sweetpotato started in 2016, and the CIP genebank’s goal is to cryopreserve 50-100 sweetpotato accessions per year.
Click here for the CIP genebank crypreservation protocols for potato and sweetpotato.
Additionally, we implemented a long-term (50+ year) viability-monitoring program for potato.
Click here for information on viability monitoring:
Each year we are cryopreserving 240 shoot tips of 10 accessions.. The shoot tips (30) are removed from LN for initial viability testing and then also repeated after 2, 4, 8, 16 and 32 years with 60 samples per accession still in the bank for future genebank managers to decide on the last two intervals (64 and 128 years ?). This experiment will allow a first look into what happens to viability of germplasm over long term storage.
Reference: For curator assistance contact with Ivan Manrique i.Manrique@cigar.org