Genetic Resources of Corn
The genetic material for any crop plant is extremely valuable. Before the early 20th century, those genetic resources were contained in farmers' fields and renewed each season when the crop grew and the seeds harvested. The Virginia Gourdseed corn grown on George Washington's Mount Vernon farm or the "criollo" corn that the Mayans grew in Chiapas, Mexico were all part of the global storehouse for the genes of corn.
Development of Genetic Resource Conservation in the US
During the 19th century, the practice of developing and maintaining particular varieties of crop plants became common. In the United States, Congress created the Department of Agriculture in 1862 "to procure, propagate, and distribute...new and valuable seeds and plants". In 1901, the Office of Foreign Seed and Plant Introduction was created in the Department of Agriculture. Its mission was to find seeds and plant material that could be useful to US agriculturalists. With the rediscovery of Mendel's principles of genetic inheritance in 1900, the science of plant breeding and the value of diverse genetic material grew.
In 1946, Congress passed the Research and Marketing Act, which established four centers that would perform research on new and useful crops, including those that could be used in chemical and manufacturing industries. There were four centers created: Ames, Iowa; Geneva, New York; Experiment, Georgia; and Pullman, Washington. Each station was responsible for plant breeding research as well as collecting and maintaining genetic materials from around the world for several crop species. The North Central Regional Plant Introduction Station in Ames, Iowa preserves the corn collection, containing over 20,000 accessions. Seeds intended for distribution are kept at 5ºC and 30% relative humidity.
In 1958, the National Seed Storage Laboratory (now called the National Center for Genetic Resources Preservation) began operating in Fort Collins, CO. This center provides an additional safekeeping site for many crop plants and their wild relatives. It keeps backup samples of materials from the regional Plant Introduction Centers as well as seeds from other governmental agencies, botanical gardens, national genebanks in other countries, international genebanks, non- governmental agencies and Native American tribes. Samples are kept under conventional storage conditions (-18ºC, low humidity) and also under cryogenic storage (in canisters of liquid nitrogen at -160ºC). Seeds stored under conventional methods can remain viable for decades and seeds maintained under cryogenic conditions should be viable for hundreds of years.
Other active collections that are not part of the National Plant Germplasm System (NPGS) exist in private or institutional collections at colleges, universities, and state agricultural experiment stations. Still other collections are held by industry, nonprofit organizations, botanical gardens, and arboreta. There is no precise information regarding the number, size, or condition of many of these mostly private collections, but it has been suggested that they probably represent a substantial germplasm pool (Office of Technology Assessment, 1985), some of which may be of considerable importance. For example, commercial crop breeders, such as DeKalb Seeds or Pioneer keep their own collections for developing hybrid seed lines.
International Genetic Resource Conservation
CIMMYT (Centro Internacional por Manteniento de Maize Y Trigo/ International Maize and Wheat Improvement Center), in El Batan in the highlands of Mexico, is an important center for the storage of maize genetic materials, especially those from tropical countries. Over 28,000 landraces are maintained at the CIMMYT facility, which was established in 1963. Scientists at CIMMYT developed many crop varieties of the Green Revolution- an effort to create high yielding hybrid varieties that would eliminate hunger in the developing world.
The newest seed preservation facility is the Svalbard Global Seed Vault near Longyearbyen, Norway. Located on island archipelago in the Arctic Ocean, the center is located under a mountain in permafrost. Seeds are maintained at -18ºC under low oxygen conditions, and the permafrost provides additional protection for seeds in case of power failure. Seeds are kept only as safe storage; there are no loans of materials. Svalbard has 17,347 accessions of Zea (corn and related wild species). The Seed Vault provides backup for seed collections from around the world.
Maintaining Healthy Seed Collections
What happens to the seeds in the storage collections? Seeds, even those kept in good storage conditions, eventually lose the ability to germinate and grow. At the Plant Introduction Stations, samples from every accession undergo germination testing about every 5 years. When seeds designated for public distribution show less than 85% germination success, the accession must be "grown out" to preserve viability. In the growout, each sample or accession is planted and pollinated under controlled conditions so that plants only breed within that accession and the gene sample remains pure to that type.
All of the storage collections described above are called ex-situ storage. This means that a representative sample of seed from a particular locality was collected and preserved in a location away from the original growing site. This is an important method to preserve materials, because duplication of samples at several storage sites decreases the risk of loss from a catastrophic event (fire, weather, or even sabotage). But there are negative aspects of ex situ storage. For example, each time an accession is regenerated, there is a risk of losing some genetic variation due to random sampling. For example, if a genetic variation is rare (for example, only 1 of 100 seeds has that characteristic), then if only 250 plants are used in the growout, it is possible that gene variant might be missed. This is especially important for characteristics not visible to the eye. The other problem with ex situ storage is that the samples are static- they are a sample of the genes at a particular time, but do not reflect any changes or responses to the environment.
For these reasons, many people believe that in situ or on-farm conservation is also important. In situ collections grow in the places where they historically occurred. These collections may be the varieties used by Andean farmers in Ecuador or the dent corn grown for generations by southern US farmers for making grits. Climate change as well as evolution of plant pests are reasons why keeping a dynamic, evolving collection of in-situ materials is important.
Anyone can help preserve crop genetic resources. In your own community, you may find families that grow a type of corn that has been in their family for generations. Farmers markets or local feed stores can be a source of information. One national organization to help get started is the Seed Savers Exchange in Decorah, Iowa. Members of this group grow varieties that may be family heirlooms and exchange them with other members.
Discovering more online:
Seed saving groups
Maintaining genetic resources at the National Center for Genetic Resources Preservation
Maintaining maize genetic resources at the international center at CIMMYT