The diversity of most of the world’s crops can be conserved over long periods simply by drying seeds and storing them under cold, dry conditions. Unfortunately, however, a significant number of crops, and in particular many crops of great importance to the poor, cannot be conserved so easily and must be stored as vegetative material. Crops such as potato, sweet potato, breadfruit, cassava, yams, coconut and banana must be conserved in this more complicated manner because they do not produce seed (they are propagated vegetatively, that is through cuttings) or their seeds are hard to store.
Compared to conventional cold storage of seeds, conserving such crops is very expensive, as the process traditionally depends on field genebanks. That means keeping fully grown plants – such as coconut palms or bananas – in the fields of a research station or botanic garden, with all that means in terms of maintenance costs and vulnerability to pests, diseases, and severe weather. The sustainability of these collections, and consequently their future role in improving agriculture for the poor, depends on the development of low-cost methods that conserve accessions cheaply out of harm’s way, but where they are readily available to breeders and researchers.
Conservation of plant cuttings in test tubes containing a growth medium and under conditions that slow down growth is an improvement over field genebanks, but still requires regular sub-culturing, and researchers have been seeking cheaper, longer-term solutions. Cryopreservation is the process by which plant tissues are conserved under extremely cold conditions, i.e. the temperature of liquid nitrogen (−196°C). At such a low temperature, biological activity is effectively halted, yet when the material is returned to warm conditions, normal cell activity starts again. Research with a number of vegetatively propagated crops, such as bananas, has been successful in developing methods for cryopreservation. Although this research, and the initial placement of genetic materials under these conditions, is expensive, cryopreservation is generally regarded as among the most secure and cost-effective long-term conservation options for many vegetatively propagated crops and crops whose seed cannot be stored dry and cold (such seeds are called “recalcitrant”, in contrast to “orthodox” seeds such as wheat and beans).
The Trust has supported research to develop or perfect cryopreservation procedures for a number of important vegetatively propagated crops: aroids (taro and relatives), cassava, sweet potato and yams. This work has contributed significantly to the cost-effective, safe, long-term conservation of the diversity of these crops.
The Trust has also supported the cryopreservation of more than 200 unique banana accessions at the Musa International Transit Centre. These accessions are part of the international collection managed by Bioversity International under Article 15 of the International Treaty on Plant Genetic Resources for Food and Agriculture. All of the accessions in the world’s largest banana collection (which numbers 1,100 accessions) which are disease-free and thus available for exchange are now safeguarded in long-term conservation and available for use by breeders and researchers worldwide.