|Cryopreservation: The future in conservation|
|Thursday, 05 January 2012 13:30|
In 2009, SPC’s Centre for Pacific Crops and Trees (CePaCT) began a cryopreservation project, funded by the Global Crop Diversity Trust. The latest results and the progress made on the cryopreservation of taro and other edible aroids were presented by the CePaCT Cryopreservation Research Technician, Ulamila Lutu, at the International Symposium on Cryopreservation of Horticultural Crops held in China from 28 June to 2 July 2011.
The symposium provided an opportunity not only to present the results of this project but also to improve on general cryopreservation guidelines through sharing information with other partners in the global cryopreservation project. Participants were impressed with the work and results achieved by SPC, and SPC was the only organisation given approval to publish a paper on the results of its work on the cryopreservation of taro and other edible aroids.
Cryopreservation is storage at ultra low temperature (–196oC), usually in liquid nitrogen. All cellular division and metabolic processes stop at this temperature, so plant material can be stored without alteration or modification for an unlimited period of time in a small volume, protected from contamination and requiring very little maintenance. Cryopreservation currently offers the only safe and cost-effective option for the long-term conservation of genetic resources of vegetatively propagated species.
Cryopreservation protocols have been developed for numerous species from both temperate and tropical origins. Once techniques are optimised, their application in genebanks ensures safe and efficient long-term storage of the germplasm of species that are important for future food and nutritional security. However, the techniques involved in cryopreservation, in particular, meristem culture, can take some time to perfect. The meristem, or shoot-tip tissue, used for cryopreservation has to be 0.8–1 mm in size; in excising tissue this small, there is always a risk of damaging it, thus killing the plant, which will affect the regeneration rate (the number of plants obtained from the cryopreserved meristems). High regeneration rates are required, both to cover the losses that might occur but, importantly, to ensure that samples can be taken to monitor viability and to provide enough plants per accession for utilisation.
A skilled technician takes approximately one hour to excise four meristems and, ideally for each accession, there should be three independent repetitions of about 55 meristems per accession. This illustrates the significant labour input required to cryopreserve collections. The more skilled the excision, the better the regeneration rate, once the cryopreservation protocol has been optimised.
Another challenge faced in this particular research project is access to liquid nitrogen (LN), which has to be purchased from a source approximately 30 miles away from Narere, where CePaCT is located, and depends on the availability of the LN supply from overseas.
CePaCT’s edible aroid collection is significant, consisting of a large in vitro collection of taro (Colocasia esculenta) — 1050 accessions — mainly from the Pacific region, but also some from Asia.
The Asian collection has been expanded with the recent addition of accessions from Indonesia; further additions from other Asian countries such as Thailand and Philippines are planned. Collections of three other edible aroids, namely Alocasia macrorrhizos, Cyrtosperma merkusii and Xanthosoma sagittifolium are being established, for example, the collection of C. merkusii, now comprises 50 accessions. The labour and utility costs to maintain these collections in good condition are high, and cryopreservation offers an excellent opportunity to reduce such costs.
The project started with intensive training provided by Dr Bart Panis and the team at the Catholic University of Leuven (KUL), Belgium in April 2009. The training coincided with the first International Symposium on Cryopreservation in Horticultural Species, which provided an excellent opportunity to learn from cryopreservation experts. Cryopreservation is relatively new to the region, with only two published reports (2001 and 2008) by Rajnesh Sant a former Research Technician at SPC in what was then known as the Regional Germplasm Centre. The 2008 publication reported the use of a droplet vitrification protocol, resulting in a 73-100% regeneration rate on a range of taro varieties.
In the current project, the droplet vitrification method described by Sant et al. (2008) was tested. Regeneration rates of 60–80% were obtained for both A. macrorrhizos and C. merkusii, and 100% for X. sagittifolium.