Cryogenic Storage of Cereal Grains: Results from a 20 Year Experiment

Authors: Walters, Christina; Wheeler, Lana; STANWOOD, PHILIP - Retired ARS Employee

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/16/2009
Publication Date: 5/1/2009
Citation: Walters, C.T., Wheeler, L.J., and Stanwood, P.C. 2009. Cryogenic Storage of Cereal Grains: Results from a 20 Year Experiment. Seed Technologists Newsletter. 83(2):22. Association of Official Seed Analysts and Society for Commercial Seed Technologists. May 29-June 4, 2009. Fort Collins, Colorado. Meeting Abstract.

Interpretive Summary: This paper compares the viability of small grains stored under conventional (-18oC) or cryogenic conditions (vapor above liquid nitrogen(LN)) for 22 to 25 years at the National Center for Genetic Resources Preservation. Several accessions of different small grains crops were split in 1984-1987, stored at the two temperatures, and assessed for viability in 2003-2008 using standard testing protocols. While some grasses known to have poor shelf life (i.e., Bromus inermis and Lolium multiflorum) showed slightly higher germination percentages after storage in LN compared to -18oC, there were no significant differences between percent germination of most grain species stored under the two conditions. However, grains of Hordeum vulgare, Sorghum bicolor, Triticum aestivum and Zea mays showed lower germination following liquid nitrogen storage compared to -18oC. A more detailed study of T. aestivum grains to determine the basis for this surprising result revealed differences in initial moisture treatments, with -18oC being stored at about 11% water while LN-stored seeds were dried to 7.5% water. This level of drying did not appear to reduce initial germination or cause imbibitional damage, but may have predisposed grains to damage by rapid cooling to LN or overdry storage. Older grains sealed in tubes and placed in vapor above LN (~40oC/min cooling) showed reduced germination compared to the same accessions cooled to vapor phase LN in an insulated container (~1oC/min). Fresh grains showed no sensitivity to cooling rate. We conclude that several variables need consideration when placing cereal grains in LN storage and that overdrying and rapid cooling should be avoided.

Technical Abstract: This paper compares the viability of small grains stored under conventional (-18oC) or cryogenic conditions (vapor above liquid nitrogen(LN)) for 22 to 25 years at the National Center for Genetic Resources Preservation. Several accessions of different small grains crops were split in 1984-1987, stored at the two temperatures, and assessed for viability in 2003-2008 using standard testing protocols. While some grasses known to have poor shelf life (i.e., Bromus inermis and Lolium multiflorum) showed slightly higher germination percentages after storage in LN compared to -18oC, there were no significant differences between percent germination of most grain species stored under the two conditions. However, grains of Hordeum vulgare, Sorghum bicolor, Triticum aestivum and Zea mays showed lower germination following liquid nitrogen storage compared to -18oC. A more detailed study of T. aestivum grains to determine the basis for this surprising result revealed differences in initial moisture treatments, with -18oC being stored at about 11% water while LN-stored seeds were dried to 7.5% water. This level of drying did not appear to reduce initial germination or cause imbibitional damage, but may have predisposed grains to damage by rapid cooling to LN or overdry storage. Older grains sealed in tubes and placed in vapor above LN (~40oC/min cooling) showed reduced germination compared to the same accessions cooled to vapor phase LN in an insulated container (~1oC/min). Fresh grains showed no sensitivity to cooling rate. We conclude that several variables need consideration when placing cereal grains in LN storage and that overdrying and rapid cooling should be avoided.