How long can seeds live?
The many popular stories of viable seeds being recovered from the tombs of ancient Egyptians are difficult to verify. However, there are a few examples of extreme seed longevity that do hold up to scientific scrutiny.
For example, a seed of Canna compacta was germinated following extraction from a radio-carbon-dated 600 year old ceremonial rattle made of a walnut (Juglans australis) shell. Even older was a seed of the Indian or sacred lotus, Nelumbo nucifera, from an ancient lake bed in China. This seed was germinated and subsequently radio-carbon-dated by Shen-Miller and colleagues in California as being 1,288 ± 271 years old.
Although the seed viability equation predicts survival for hundreds to thousands of years under gene-bank conditions (15% RH, -20°C), there are only a handful of credible reports of seeds actually surviving for ≥150 years. Recently we have conducted germination tests on seeds of 33 South African species collected in 1802/3. The seeds were found at the National Archives in London among the papers of a Dutch merchant, Jan Teerlink, whose ship was captured by British privateers during its return from the Far East via the Cape of Good Hope, South Africa. Seeds of three species germinated: two legumes (Liparia sp. and Acacia sp.) and a Proteaceae (Leucospermum sp.). Our report in Seed Science Research (see below) of seeds surviving for over 200 years (supported by carbon-dating) under sub-optimal conditions, suggests adaptation for extreme seed longevity in species of seasonally dry Mediterranean environments.
MSBP scientists have been studying species differences in seed longevity using controlled ageing experiments. These experiments have revealed that seeds with small embryos from plants that grow in cool, moist environments are more likely to be short lived compared to seeds with large embryos that come from warmer drier regions.
Predicting how long seeds will survive under different storage conditions
The viability equations are mathematical models that have been developed to predict seed storage life in different environments. They are used by gene banks to help design and manage seed storage facilities. But they can also be applied to local conditions.
For example, a forest extension officer working with communities in Burkina Faso to collect and plant Khaya senegalensis, a multipurpose tree species with an oil content of 67%, can use the viability equations to help estimate how long seeds will survive in the community tree seed bank.
Khaya senegalensis seeds are shed during the month of May, when the average daily temperature is 32°C and relative humidity is 52% RH. Ambient drying during the afternoon (x°C, 40% RH) brings seed moisture level down to 40% eRH. Seeds are then stored at an ambient temperature of around 29°C in large plastic drums. An initial germination test shows that viability is 99%. Using the viability equations the extension officer can estimate that the seed viability after 12 months storage under these conditions will be 67%. He can also work out that if he used charcoal to dry seeds to 25% eRH and then stored them in the same way, viability after 1 year would be 90%.
Learn how to use the viability equations
Daws, M.I., Davies, J., Vaes, E., van Gelder, R. & Pritchard, H.W. (2007) Two-hundred-year seed survival of Leucospermum and two other woody species from the Cape Floristic region, South Africa. Seed Science Research 17: 73-79.
Probert, R.J., Daws, M.I. & Hay, F.R. (2009) Ecological correlates of ex situ seed longevity: a comparative study on 195 species. Annals of Botany 104, (1), 57–69.
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