**7. Cryopreservation**

Cryopreservation is the storage of plant materials at ultra-low temperatures in liquid nitrogen (-196o C). The plant cells kept at this low temperature are devoid of metabolic activities and cell division. Therefore, the materials can be kept or stored for long time without any changes in their cellular structure [20].

Cryopreservation can be a primary or secondary storage technique. For certain plant materials such as embryonic culture that lose their capacity to move to the next stage of embryo formation, it could be a form of primary storage. When used for the conservation of plant genetic resources, it is a secondary storage form and usually as a form of backup or reserve for plant species [21]. The prospect of cryogenic technology is promising as it is important in conservation of genetic uniformity, preservation of rare genomes, sustaining disease-free plant materials, maintenance of morphogenetic potentials, and delaying aging of plant materials. The above techniques are all forms of secondary storage, which have tremendous commercial benefits [19, 21].
