Updated 04/18/02


Welcome to the National Seed Storage Laboratory, part of the National Center for Genetic Resources Preservation in Fort Collins, Colorado. You've already read why we store germplasm, now come and see how we handle and store the valuable materials when they arrive. Take a look inside the vaults to see both conventional and liquid nitrogen (cryogenic) storage.

seeds from around the worldSEED AND PLANT MATERIAL DONORS/SOURCES:

NSSL receives seed and plant materials from all over the United States and the world. NSSL stores the base collection of the National Plant Germplasm System. NSSL also works with international organizations such as the International Maize and Wheat Improvement Center (CIMMYT - Mexico), the International Rice Research Institute (IRRI - Philippines) and the International Plant Genetic Resources Institute (IPGRI - Rome), as well as the Centers for Plant Conservation (CPC), the Crop Science Society of America for Crop Science Registration (CSR), and the Plant Variety Protection Office (PVPO).



Quarantine is a government program to monitor and control the importation of plant and animal materials. Samples that arrive at NSSL under quarantine restrictions are handled in the quarantine laboratory.

Samples are inspected and prepared for storage in a laminar flow biological safety cabinet. Material being prepared for increase is surface sterilized and treated with a fungicide prior to shipment. All germplasm is increased and inspected for disease and/or insect infestations by APHIS inspectors on the island of St. Croix (a substation for the Tropical Agriculture Research Station in MayagŁez) or other approved sites prior to release into the National Plant Germplasm System.



Each sample is inventoried and barcoded
Upon receipt of seed samples, information is verified with GRIN, NSSL serial numbers are assigned, germination cards and bar code labels are printed. After unpacking, samples are placed in an equilibration room with 23% relative humidity at 5° C. Samples are equilibrated for a few weeks to achieve the optimum moisture content for storage.



Seed blower being used by Seed AnalystAfter optimal moisture content is achieved, seed analysts remove inert material, empty seeds and contaminating seeds (i.e. weed seeds). Seed blowers such as this one remove all light material and chaff, leaving only the heavy seed. Seed may also be cleaned through the use of sieves and/or rubbing boards.



VACUUM PLANTERS AID IN PLANTINGViability assessment means testing the sample to determine how many seeds are alive. Analysts assess viability using the germination and tetrazolium tests.




SEEDS ARE GERMINATED ON BLOTTER TOWELSAnalysts select appropriate conditions and plant a subsample of the pure seed on standard germination blotters or towels. The number of seeds tested is dependent on the size of the sample. All samples scheduled for cryogenic storage in liquid nitrogen have paired tests performed to check for damage caused by the liquid nitrogen (LN2). The LN2 test exposes some of the seed for 24 hours to the vapor phase of LN2 (approximately -160° C, or -320° F). Seedling evaluation of the germinated seeds follows the "Rules of Testing Seed" of the Association of Official Seed Analysis Seedling Evaluation Handbook. Abnormalities and pathogen problems are assessed.

Moisture content, viability, cleanout, and seed counts are tracked and results uploaded to GRIN.



Seed of certain kinds of plants do not produce a plant that is genetically identical to the parent. To preserve this plant material, we need to store buds or meristematic tissue that will later be grafted onto other plants or grown in a petri dish to produce small plantlets. Fruit trees, potatoes, and sweet potatoes are examples of species that can be stored this way. NSSL is storing apple buds cryogenically on a routine basis. Buds are more sensitive than seeds to rapid cooling so special protocols have been developed to bring the buds down to the low temperature of liquid nitrogen vapor without harm to the buds.



NSSL stores samples in conventional storage at -18° C and cryogenic storage using liquid nitrogen at -196° C (-160° C in the vapor phase). Storage method is determined by the type of seed, the size of the seed, the number of seeds in the sample, the viability of the sample, and sometimes the instructions from the donor.

SAMPLES ARE BARCODED FOR NSSL NUMBER AND STORAGE LOCATIONSamples stored by conventional methods are transferred to heat sealable, moisture-proof, foil laminated bags. Locations are assigned and barcodes for the location and serial numbers are placed inside and on the outside of the bags. The bags are then heat sealed and placed in trays in the cold storage vault.
Samples stored by cryogenic methods are transferred to clear polyolefin tubes, barcoded, and closed with birchwood plugs. There is no free water in liquid nitrogen, so samples are not in danger of increasing their moisture content. Filled tubes are then placed in metal boxes, labeled with serial numbers and locations, and stored in the LN2 tanks.



The vault area at NSSL is a separately constructed portion of the building, self-contained with it's own air handling unit and electrical generator in case of emergency. It is able to withstand possible floods from nearby Horsetooth Reservoir, tornadoes, and the dropping of a 2500 pound object traveling at 125 miles per hour. The vaults have the capacity to store 1.5 million samples, 50% in conventional storage, and 50% in liquid nitrogen.



The individual storage units have walls with six inches of insulation and are metal covered. Temperature is kept at -18° C.

This vault is 5000 square feet. The samples are stored in plastic trays on shelves which are part of a moveable rack system, which allows for a 60% greater room capacity over the old multiple aisle system. As each carriage is moved, the light from the previous aisle is turned off and the light above the newly opened aisle is turned on.  

The life expectancy of a seed sample stored in this vault is from 20 to 50 years. Because of the variability of seed longevity, periodic retesting is done to identify regeneration needs.


SEED ANALYST FILLING A LN2 TANKTwo floors of the vault area are designed for cryogenic storage. One is in current use, and the other is designed for expansion. Each floor can hold 112 storage tanks, and has double-walled stainless steel piping for filling from the 13,000 gallon tanks located outside the building.

Cryotanks are like giant thermos jugs with vacuum jacketed double walled insulation. Each tank will hold 330 metal containers (metal boxes containing tubes of seed samples) on a lazy susan which holds the samples above the liquid nitrogen and allows easy access to each section. A tank holding wheat could contain 2640 samples, whereas a tank of tobacco (a very tiny seed) would contain 26,400 samples. We try to have a minimum of 3000 seeds per sample for cross pollinated crops and 1500 seeds for self pollinated crops.

Tanks are filled once a week, with about 56 liters of liquid nitrogen.

Air circulation is very important in the vault since nitrogen gas is constantly boiling from the tanks. Oxygen monitors are placed around the vault for detection of oxygen content of the air. Emergency fans are triggered by the oxygen monitors or emergency buttons. During an emergency, liquid nitrogen is shut off and fans provide 14 air exchanges per hour.

All of these elaborate precautions are to ensure that our valuable germplasm lives as long as possible, and is available for plant breeders and researchers to produce the food and fiber products we all depend upon.   


 Send Orders for Germplasm to: orders@ars-grin.gov
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