Germplasm Storage - Conservation of plant genetic resources or germplasm by several national (National Bureau of Plant Genetic Resources = NBPGR) and international organizations (International Board of Plant Genetic Resources = IBPGR, now renamed as International Plant Genetic Resources Institute = IPGRI) has become a thrust area of biotechnology in recent years. For this purpose, various strategies for storage of germplasm without losing its viability have been developed and are being utilized.

Germplasm can be stored in a variety of forms including seeds, buds, protoplasts, cells, tissues, etc. Well organized plant parts like shoot tips and plantlets in culture can also be used for long term storage. The techniques involving storage of tissues in culture may use the germplasm in the growing stage and their growth may be suspended, by anyone of the following methods:
(i) lowering the temperature,

(ii) adding chemical retardants or hormones and

(iii) reduction in oxygen concentration.

The germplasm can be used whenever required. Examples of storage of plant tissue culture (condensed from Withers, 1983) rapid thawing. Pollen required for hybridization can also be cryopreserved. For cryopreservation, cells in early exponential phase have been found to be the most highly freeze tolerant, while those in lag phase or stationary phase are susceptible to some freezing injury.

This susceptibility to freezing injury actually depends on the size of individual cells and also on the size of aggregates or clumps used for cryopreservation. Callus cultures, cell suspensions, zygotic embryos (from wide crosses) and somatic embryos, all can be used for cryopreservation.