Saving seeds: Optimally planning our Ex Situ conservation collections to ensure species' evolutionary potential

Abstract

In the face of ongoing environmental change, conservation and natural resource agencies are initiating or expanding ex situ seed collections from natural plant populations. Seed collections have many uses, including in provenance trials, breeding programs, seed orchards, gene banks for long-term conservation (live plants or seeds), restoration, reforestation, and scientific study of plant germination or other plant ecology studies. Well-known examples of ex situ collections include the Millennium Seed Bank Partnership, Australian Seed Bank Partnership, United Kingdom National Tree Seed Program, United States National Plant Germplasm System, and South African Regional Seed Bank. Some collections focus on rare species, species with relevance to agriculture or forestry, or regional flora. Other collections are in response to immediate threats, such as damaging insects and pathogens (e.g., emerald ash borer). In this talk I will discuss how to sample seeds to most optimally conserve the evolutionary potential of a species to ensure its long-term survival. A useful seed collection captures as much phenotypic and genetic diversity from natural populations as possible. Choices for a collector include how many populations, maternal plants, and seeds per plant to collect. A collector wishes to achieve efficiency—to not waste limited time, resources, personnel, and storage space, but also to achieve effectiveness—to be as complete as possible in case important genetic variants are lost from natural populations. In a series of papers starting in 1975, Brown and Marshall (1975) proposed some solutions to this general sampling problem. They used simple mathematical equations to derive a minimum number of samples needed to capture allelic variants that occur in a population at a given minimum frequency. For an arbitrary minimum frequency of 0.05, the recommended minimum sample size was 30 individuals from a fully outcrossing species or 59 individuals from a fully self-pollinating species. A ‘rule of thumb’ of 50 samples was suggested for practical use. This 50 sample guideline has since been integrated into many protocols for sampling seed, and is still common 4 decades later. Hoban and Strand (2015) found this guideline cited in 60 percent of protocols from major seed collecting or natural resource management organizations.

Parent Publication

• Gene conservation of tree species—banking on the future. Proceedings of a workshop.

Citation

Hoban, Sean M. 2017. Saving seeds: Optimally planning our Ex Situ conservation collections to ensure species' evolutionary potential. In: Sniezko, Richard A.; Man, Gary; Hipkins, Valerie; Woeste, Keith; Gwaze, David; Kliejunas, John T.; McTeague, Brianna A., tech. cords. 2017. Gene conservation of tree species—banking on the future. Proceedings of a workshop. Gen. Tech. Rep. PNW-GTR-963. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 137-141.