Seed germplasm preservation using liquid nitrogen

Abstract

Liquid nitrogen (LN(,2)) storage of valuable seed germplasm has the potential of providing indefinite preservation. The capability of seed of a given species or selection to withstand cooling to LN(,2)(-196 deg C) and subsequent rewarming without damage is a critical first and major step to the practical application of this preservation technique. Over 120 species representing agronomic, vegetable, flower, shrub and tree species were cooled to LN(,2) and rewarmed without loss of viability. Variability within species to resist LN(,2) damage appeared to be normal except in flax (Linum usitatissimum) and sesame (Sesamum indicum) seed. Mechanical reliability and stability of LN(,2) refrigeration systems are very good, resulting in improved quality of storage conditions relative to conventional systems. Cost advantages using LN(,2) storage can also be achieved, especially if the seed size is equal to or smaller than cotton seed. Additional cost advantages can also be realized if sample handling, viability monitoring and replenishment/regrowing costs are also considered. The biological, mechanical and cost feasibility are favourable for the use of LN(,2) as a long-term storage medium for seed germplasm. The duration which the seed can be held in LN(,2) without loss of viability is unknown and will be unknown for many years. However, the potential is considerable and may provide a much better quality of seed and improve maintenance of plant genetic resources.