The role of ex situ seed banks in studies of temporal variation in natural populations
Ex situ seed banks are an accepted and essential strategy for ensuring access to diverse genetic resources for crop improvement or conservation. Using seed banks as a tool to address evolutionary questions is a new application. Implicit to all seed banking activities is the requirement that the process of seed banking does not affect the viability or genetic identity of the accession. Loss of seed viability during storage can result in genetic drift or inadvertent selection of traits associated with longevity, such as seed maturity or hard-seededness. Predicting how long seeds will survive determines how comparisons between past and future seed collections can be interpreted and ultimately provides sidebars on the utility of the Project Baseline approach.
Based on long-term data sets of seeds of crops and their wild relatives, we estimate that 100 years is an average expectation for shelf life under the storage conditions used at NCGRP (20% RH and -18oC); however, variation within and among species is substantial. So far, the Project Baseline collection at NCGRP consists of 165 accessions representing 27 species with an average of 6 populations per species. Initial seed quality ranges substantially among species and populations. Our lab is conducting simulated aging studies to help predict the shelf-life of these seeds both in an ex situ seed bank under highly controlled conditions to maximize seed longevity and under soil seed bank conditions where longevity is expected to be shorter. Our work to document temporal variation of wild barley (Hordeum vulgaris spp. spontaneum) collected as seeds from populations in Jordan in the early 1980s (and stored ex situ) and again in 2012 may provide insight into how Project Baseline can address questions of plant adaptation to climate change.