How long can seeds live? The life of a seed varies according to the species and the conditions it has been stored in. There are many stories of the germination of seeds removed from ancient Egyptian tombs. To the best of our knowledge, none of these stories is strongly supported by archaeological evidence of the antiquity of the seeds. This aside, the conditions within Egyptian pyramids are very dry and would permit seed longevity in certain species to extend to thousands of years. Nearly all of the records of extreme longevity relate to seeds with hard coats (or testas). Seed viability has been modelled for some 70 species and it is possible to predict their longevity, given moisture content, temperature and initial germination.These models have been developed by rapidly ageing batches of seeds at a range of high moisture contents and high temperatures, and then plotting their loss of viability. Extrapolation (often a risky procedure) to viability loss under more favourable storage conditions suggests that, for instance, mung beans might live for nearly 24,000 years, and the African grass, teff (Eragrostis tef), could live for 15,000 years. Not surprisingly, few longevity experiments of any age that mirror seed conservation storage are available for us to study today. However, in 1987, samples of cereal and weed seeds were germinated that had been placed within sealed glass vials in Vienna 110 years earlier (reported by Steiner & Ruckenbauer in 1995). One of the aims of the Millennium Seed Bank Partnership is to set up a carefully controlled set of longevity experiments that future generations can study. 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 more than 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 (reference 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. Other examples of extreme longevity include a seed of Canna compacta that was reported to be germinated following extraction from inside a radio-carbon-dated 600 years old ceremonial rattle made of a walnut (Juglans australis) shell. Even older longevity has been reported in a seed of the Indian or sacred lotus Nelumbo nucifera from an ancient lake bed in China. This seed has been germinated and subsequently radio-carbon-dated by Shen-Miller and colleagues in California as being 1,288 ± 271 years old. An interesting story relates to seeds of the legume Albizzia julibrissin on a pressed herbarium specimen collected from China in 1793 and deposited in the British Museum. This specimen was watered while a fire was being extinguished in 1940 and several seeds (at least 147 years old) germinated. Seed longevity in the soil is also well known to gardeners. In regions where the soil retains a high level of moisture, most (non-hard-coated) seeds will survive in a hydrated state, not in a dry state as in seed stores. For them to survive in this wet state they must be able to respire and must possess dormancy that prevents germination. In 1879, W.J. Beal, in Michigan, buried samples of seeds of 23 species in moist sand as an experiment in soil seed bank longevity. Seeds of the moth mullein (Verbascum blattaria) from this experiment germinated in 1970. Further information: 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.
Posted on: Mon, 31 Mar 2014 11:23:26 +0000
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