Submitted to: Seed Science Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/1/2004
Publication Date: 3/1/2005
Citation: Walters, C.T., Wheeler, L.J., Grotenhuis, J.A., 2005. Longevity of seeds stored in a genebank: Species characteristics. Seed Science Research 15:1-20. Interpretive Summary: Currently there is no way to predict how long a seed lot will survive in storage. Unscheduled decreases in seed viability can result in losses of valuable breeding stock or germplasm. Investments in storage facilities to prolong shelf life of seeds that are inherently long-lived may be unnecessary. The first step in predicting how well a seed lot will perform is to understand general storage characteristics of the species. This paper consolidates and quantifies germination monitoring data from the USDA National Plant Germplasm System collection for 168 plant species and provides estimates for how long a seed may be expected to survive under conditions used at the National Center for Genetic Resources Preservation. We show that seeds stored predominantly at 5C (temperature typical for a refrigerator) will maintain > 50% viability for about 52 years, but average longevity can range from 12 to 466 years depending on species. Reducing storage temperature to -18C (temperature typical for a freezer) will likely increase the expected longevity. Despite extended shelf lives of seeds achieved under genebanking conditions, the variability in longevity among individual samples is considerable, and the basis of this variation is currently under investigation.
Technical Abstract: Seed species are believed to have characteristic shelf lives, though data confirming this are scarce and a mechanistic understanding of why this would be remains elusive. We have quantified storage performance of over 38,000 accessions of seeds representing 168 species within the USDA National Plant Germplasm System (NPGS) collection as well as a smaller experiment of 207 cultivars from 42 species. Accessions from the NPGS collection were harvested between 1934 and 1975 and had relatively high initial germination percentages that decreased at a variable rate during storage at 5 and -18C. Germination time courses that represent average performance of the species were fit to Avrami kinetics in order to calculate the time at which germination characteristically declined to 50% (P50). Values of P50 correlated among different longevity surveys conducted under controlled conditions; but there was no correlation among these studies and seed persistence in the soil. Some plant families had characteristically short- (e.g. Apiaceae and Brassicaceae) or long- (e.g. Malvaceae and Chenopodiaceae) lived seeds and seeds of species originating from some areas had characteristically short- (e.g. Europe) or long- (e.g. South Asia) shelf lives. However, there appeared to be no correlation between longevity and dry matter reserves, soluble carbohydrates, and parameters relating to soil persistence or resource allocation. Though data from this survey supports the hypothesis that some species tend to survive longer than others in a genebank environment, there is little information on the attributes of the seed that affect its storage performance.