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item Towill, Leigh

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 6/6/2004
Publication Date: 10/1/2004
Citation: Towill, L.E. 2005. Germplasm preservation. pp. 277-284. In R.N. Trigiano and D.J. Gray (eds) Plant Development and Biotechnology. CRC Press, Boca Raton, FL.

Interpretive Summary: The preservation of diversity allows materials to be used over time. Plant tissue culture methods complement traditional methods for species that are maintained either as seed or as vegetative plants. The germplasm of many species is held as seed. Desiccation-tolerant seed is easy to store and both lower temperatures and moisture contents increase longevity. Tissue culture is not usually used for the preservation of this group. Desiccation-sensitive seed have short longevities, and tissue culture techniques are used to establish plant cultures or retrieve isolated axes after cryogenic storage. The latter is often feasible if moisture content is adjusted to a critical range. Plants that are maintained vegetatively, usually in the field or greenhouse, also benefit from tissue culture methods. The establishment of in vitro plants and their maintenance is more economical and space saving. Cryogenic storage of shoot tips from the latter or embryonic axes from recalcitrant seed provides long-term preservation. Methodologies to achieve high survival percentages require optimizing several steps, including preculture acclimation, cryoprotectant exposure, cooling and warming rates, removal of cryoprotectants, and recovery media.

Technical Abstract: Germplasm contains the diversity of genotypes needed to develop new and improved lines. Its preservation assures availability for use over time, and is usually accomplished using seeds or vegetative plants. Species that have desiccation-tolerant seed are preserved by adjusting seed moisture to an optimum value and then storing at low temperatures. Longevity depends upon species, quality of the seed and storage conditions. Often temperature of -5 degrees C to -20 degrees C provide considerable longevity. Cryogenic storage, in concept, should provide the greatest longevity and for tolerant seed is relatively simple if the moisture content is fairly low. Desiccation-sensitive seed, however, have short longevities and do not tolerate extensive moisture loss. Species possessing this type of seed are often stored as vegetative plants, although recent studies using embryonic axes and moisture adjustment to a critical value demonstrate that they may survive cryogenic exposure. Plant tissue culture supplements preservation for these whereby in vitro plants can be established and held, and excised embryonic axes are cultured after storage to generate the plant. Tissue culture is most valuable for plants maintained as clones. Maintenance of in vitro genebanks saves space, allows rapid propagation and is more economical. Shoot tips from either field or in vitro plants can be cryopreserved using a detailed methodology. In many cases the shoot tip is retrieved after cryogenic storage by tissue culture techniques and induced to develop into a plant.