The storage conditions, mainly water content and temperature, are the crucial factors affecting seed longevity, although genetic features and initial seed quality may also have a relevant influence.
The seed conservation process of the CRF genebank comprises the following stages:
- Registration of the samples and seed cleaning
- Seed drying in desiccation chambers (15% R.H. and 20ºC)
- Determination of the initial seed viability via germination tests
- Seed packaging in airtight containers (metal cans for the base collection and glass jars for the active collection)
- Storage in cold chambers: at -18ºC and -4ºC for the base and active collection, respectively
- Seed viability monitoring every ten years – or longer periods, depending on the species-
- Distribution of seed samples to users
At present (September 2020) the base and active collections of the CRF genebank hold 22,364 and 44,127 accessions, respectively, from over 400 botanical genera.
In the period 2015-2019, 18,780 germination assays were conducted, including initial tests (30.7%) and periodic monitoring (69.3%). In the last 5 years an average of 1,432 samples/year have been sent for research, breeding, education and cultivation purposes.
The effect of oxygen on seed storage
The role of oxygen in the processes of seed deterioration has been little studied because it has been considered a less relevant factor than temperature and humidity. However, in last years there has been a growing interest in this aspect, as some studies have shown benefits in the conservation of seeds under free-oxigen environments. Since 2017, an experiment is being conducted to study the influence of different gaseous environments (air, vacum, N2, CO2, air + oxygen absorber) on seed longevity. Seed germination and seed vigor are periodically evaluated in each storage environment. Biochemical compounds associated with seed aging and oxidative damage are also analysed.
The results obtained so far seem to confirm a seed longevity increase in some of the oxygen-free environments tested.
Optimization of germination protocols
In genebanks, seed viability monitoring is a key activity to prevent genetic erosion of the conserved material. This task is carried out via germination tests that must be performed under optimal conditions, in order to achieve the complete germination of all the viable seeds. In the CRF, germination tests are usually made following the rules of the International Seed Testing Association (ISTA), which are mainly addressed to commercial varieties of cultivated species.
Estimating the viability of seeds via germination assays is more difficult in wild species because they commonly undergo seed dormancy, and appreciable variation may exist between populations of the same species. For this reason, optimizing the germination procedures of the wild species represented in the CRF genebank is one of the research areas of the Conservation Group. In the last five years, germination protocols for species of grasses and aromatic-medicinal species, among others, have been established.
Analysis of seed conservation in the CRF genebank
Germination data obtained from the CRF genebank are stored in a database that currently contains more than 122,000 records. The analysis of these data has allowed to determine differences in longevity between species and to adjust viability monitoring periods.
In 2020, the first germination data after 40 years of conservation were obtained, for accessions of grass pea, lentils, wheat, beans and vetches. The average percentages of germination obtained on these samples were 86.9 and 92.8 % in the active and base collection respectively.