Some seeds, for example those of many tropical crops, cannot be dried for storage. In addition, some crop plants, such as banana and garlic, do not usually produce seeds and are propagated vegetatively. And some species do not breed true from seed anyway and so are conserved as clones. In all these cases, to conserve the genotype, the particular combination of genes that gives a variety its characteristics, the whole plant must somehow be conserved. Some collections are kept in field genebanks, as full-grown plants, and others as tissue culture, as micro-plants growing in vitro (in test tubes). The most cost-effective way to store these accessions for the long term is through use of cryopreservation techniques, which deep freezes the material at minus 196°C in liquid nitrogen.
Although some accessions are already stored as cryopreserved samples, there is huge scope for further development of cryopreservation protocols to include more genotypes and species. Large cryobanks are vastly more secure than other forms of conservation for these crops and provide an important opportunity to allow the rationalization of field and tissue culture collections.