Seed Bank

Seed Bank

NS/S utilizes a two-pronged approach to conserving crop genetic resources from the southwestern US and northwestern Mexico. Ex situ approaches involve conserving samples of crop seeds under frozen storage conditions, where they may remain viable (able to germinate) for long periods of time. We also utilize in situ approaches that support and encourage the ongoing relationship between people and plants through which both natural and human selection pressures continue to result in the development of new crop varieties – the same relationship between people and plants that produced the diversity present today.

The NS/S Seed Bank is at the core of our conservation efforts. It serves as a repository for seeds, guarded in a safe environment for the proverbial "rainy day". In this case, the rainy day is when a crop can no longer be found growing in a farmer's field. Domesticated crops depend on an intimate relationship with humans - they don't exist in the wild. Over thousands of years, traditional agriculturists have selected and saved seed from plants that expressed a diversity of traits of interest to them or their communities - the ability to mature before the first frost, a sweeter taste, faster cooking time, or resistance to specific insects or diseases. Local, regional and global food security depends on this diversity. A seed bank's primary function is to conserve this genetic diversity for the future.

Glossary of Terms

The terms used here are from Geneflow: A publication about the Earth's Genetic Resources, produced annually by Bioversity International.

Accession: Plant sample, strain or population held in a genebank or breeding program for conservation or use.

Biodiversity: The total variability within and among species of all living organisms and their habitats.

Ex Situ Conservation: Conservation of a plant outside of its original or natural habitat.

Genebank: Facility where germplasm is stored in the form of seeds, pollen, etc., or in the case of a field genebank, as plants growing in the field.

Gene Pool: All the genes and their different alleles present in an interbreeding population.

Genetic Diversity: The genetic variation present in a population or species.

Genetic Erosion: Loss of genetic diversity between and within populations of the same species over time or reduction of the genetic base of a species due to human intervention, environmental changes, etc.

Genetic Resources: Genetic material of plants, animals, and other organisms which is of value as a resource for present and future generations.

Genotype: (1) The genetic constitution of an organism. (2) A group of organisms with similar genetic constitutions.

Germplasm: A set of genotypes that may be conserved or used, e.g., seeds, clones, pollen.

In Situ Conservation: Conservation of plants or animals in areas where they developed their distinctive properties, i.e., in the wild or in farmers' fields.

Indigenous/Local Knowledge: Knowledge that develops in a particular area and accumulates over time through being handed down from generation to generation.

Landraces: Farmer-developed varieties of crop plants that are adapted to local environmental conditions.

Plant Genetic Resources: The genetic material of plants, which determines their characteristics and hence their ability to adapt and survive.

Regeneration: The growing out of a sample from an accession to replenish the original accession's viability.

Wild Relative: A non-cultivated species which is more or less closely related to a crop species (usually in the same genus). It is not normally used for agriculture but can occur in agro-ecosystems (e.g., as a weed or a component of pasture or grazing lands).

The seed bank houses approximately 1,900 different accessions of traditional crops utilized as food, fiber and dye by the Apache, Chemehuevi, Cocopah, Gila River Pima, Guarijio, Havasupai, Hopi, Maricopa, Mayo, Mojave, Mountain Pima, Navajo, Paiute, Puebloan, Tarahumara, Tohono O'odham, Yaqui, and other cultures.

Over one-half of the accessions are comprised of the three sisters -- corn, bean, and squash. Nearly 100 additional species of crops and crop wild relatives are being preserved in the NS/S Seed Bank, including unique and often rare crop varieties: red-seeded amaranth used to dye piki bread; black-seeded sunflowers used as a dye stuff; drought-tolerant beans grown in the Pinacate region in northwestern Mexico (perhaps one of the hottest regions in North America); Sonoran panic grass (Panicum sonorum) - once thought extinct; sunflowers containing genes for resistance to a commercially devastating sunflower rust; other sunflowers that are restricted to serpentine soils; lemon basil; chia - an important source of protein, oil, and fiber; red-seeded watermelons. All these and more contribute to the rich genetic legacy maintained by the many people and cultures that have inhabited and survived among the coastal deltas, lowland plains, bajadas, and high mountain plateaus contained within the southwestern U.S. and northwestern Mexico.

Each accession represents a specific crop "variety" grown by a particular farmer and is individually preserved and maintained. These landrace, folk or farmers varieties result from both natural and farmer selection pressures over time. Sealed samples of individual accessions are placed in frozen storage. When these samples begin to show decreased viability, they are regenerated. Regeneration involves removing the sample from the freezer, growing it at the Conservation Farm and replacing the previous frozen sample with newly produced fresh seed. For each accession, duplicate samples are taken in order to have a back-up in case any individual regeneration attempt fails.

Two of the key challenges to successful regeneration involve maintaining the genetic purity and integrity of each accession. The genetic purity of an accession is maintained by preventing cross-pollination between different accessions of the same crop, such as between different corn varieties, and accidental mixing of accessions during collection, storage, harvest or post-harvest processing. We take many precautions to ensure each sample is correctly labeled, seeds are not picked up off the floor, and equipment is cleaned between each use. The “genetic make-up”, i.e., the specific combination of genes and their frequency, constitutes the genetic integrity of a sample and is considerably more difficult to ensure, particularly over long periods of time. Periodic regeneration and appropriate sampling protocols, such as saving seeds from many different parents, are the primary strategies we utilize to maximize the likelihood of maintaining the genetic integrity of each accession. When the seeds from only a few individuals form the basis of the long-term sample, a genetic bottleneck may result. A bottleneck occurs when a subset of individuals come to represent a larger population. An integral part of our regeneration efforts includes taking care to select a random sample for storage and not to inadvertently impose our own biases relative to seed size, shape, or color.

Even under frozen storage in a seed bank, seeds lose viability over time. Regenerating aging freezer samples by growing them in the field and producing new healthy, viable seed occurs at the NS/S Conservation Farm in Patagonia, AZ. Purchased in 1997, the Conservation Farm compliments the Seed Bank, which together constitute the basis of our ex situ program.