Some definitions
Throughout this course, we will be referring to the science that underpins operations used by genebanks. Here are the most important terms:
Seed viability is whether seeds have the potential to germinate or not. This is usually determined by a germination test, although sometimes another viability test can be used e.g. topographical tetrazolium staining test.
Seed longevity is the length of time seeds remain alive in a given storage environment. A measure of longevity is p50: the length of time (‘period’, p) that it takes for the viability of a seed lot to fall to 50% in a given storage environment.
Germination is the development of a new plant from a seed.
Seed moisture content tells us how much of the seed mass is actually water. It is usually expressed as a percentage of the total mass of the seed sample.
Seed water activity is another measure of water inside the seed. It is calculated as the vapor pressure of the sample – in our case of seeds – relative to the vapor pressure of pure water. It is usually expressed on a scale of zero to one. We also refer to water activity as ‘equilibrium relative humidity’ or ‘eRH’, where the scale goes from zero to one hundred (i.e., we multiply the water activity reading by one hundred). Water activity matters, because it can inform us about the physiological processes that may be occurring in the seeds.
Contemporary genebanks have their own specialist vocabulary, operations, and aspirations. Look at the terms below, and make sure you’re familiar with them.
| Term | Meaning |
| Accession | A genebank accession is a sample of plant material that is conserved to represent a particular variety, line or population. |
| Seed lot | A seed lot is a population of seeds, usually originating from the same harvest. |
| Active and base collection | In many genebanks, storage takes place in an active (medium-term) and base (long-term) collection. The active collection is the store from which samples are taken for distribution. The base collection is for long-term conservation. |
| Characterization | The process of characterization allows genebanks to describe accessions accurately, and understand their heritable characteristics. |
| Distribution | Distribution is the process of sharing accessions with users, so that their helpful traits can be harnessed, and new lines developed. |
| Orthodox seeds | Seeds that can be dried, without damage, to low moisture contents are called Orthodox seeds. Over a wide range of storage environments, their longevity increases with reductions in moisture content and temperature. |
| Recalcitrant seeds | Recalcitrant seeds do not survive drying to any large degree, and are therefore not suitable for long-term storage, although the critical moisture level they need for survival varies among species. |
| Intermediate seeds | Intermediate seeds are more tolerant of desiccation than recalcitrant seeds, though their tolerance is much more limited than orthodox seeds. It is not easy to predict how drying and cooling will affect their longevity, and they tend to lose viability more rapidly at low temperature. |
Overview of genebank processes