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Theme: Preservation Technology

Stephanie Miles holding a jar of banked seeds in the seed bank at Wakehurst Place

Conventional (orthodox) seed bank storage involves sealing dried seeds (4-7% moisture content) within air-tight containers and placing them at low temperature (-20°C). Routine germination tests are carried out in order to ensure that the collections maintain a high level of viability. Under these storage conditions it is predicted that seeds of many species will remain viable for many decades, if not hundreds or even thousands, of years. However, as this potential difference in longevity is of one or two orders of magnitude; a continued focus of this sector will be identifying taxa (at the family- / genus-level) which are particularly short-lived (in order to advise on re-testing schedules) and looking for correlates / predictors of relative longevity (e.g. seed composition, seed size / structure, habitat, distribution, climate).

Storage at a wider range of moisture contents and temperatures [including long-term, low-temperature (sub-zero down to LN­2) storage experiments] will provide confirmation (or otherwise) that relative (comparing across taxa) seed longevity does not significantly differ with storage environment; will enhance our understanding of how these two variables determine seed longevity; provide further information on optimum storage conditions for maximising seed longevity. Since moisture sorption relations and how they change with temperature (e.g. ageing cf. seed bank storage) are fundamental to our understanding of what metabolic processes (e.g. ageing, repair) may take place, accurate determination of seed equilibrium relative humidity and moisture content is a vital component of this sector’s work.

Whilst the MSBP has been primarily focused on the storage of orthodox seeds, cryobiological studies will be carried out on species with desiccation sensitive seeds; the development and transfer of cryobiological conservation methodologies is a component of the Global Strategy for Plant Conservation.  

Significant achievements (2000-05)

A major achievement has been to rank more than 160 species (mostly from families previously unstudied in this respect) in terms of seed longevity in dry storage. This has enabled us to consider relationships between seed longevity and other traits such as seed structure, climate of origin, and habitat.

We have delivered major reviews on seed bank design, trialled and introduced silica gel sachets for routine monitoring of container performance, and developed a new system for seed moisture control using lithium chloride solutions, which is routinely used in ageing experiments carried out here and by MSBP partners.

We have also reported contrasting responses to ultra-dry and frozen storage in cacti, willow and neem seed and developed cryopreservation methods for storing orchid seeds with their symbionts.

Projects on this theme:

• Comparative Longevity (Orthodox Seeds)
• Maximising Longevity in Orchids and other Socio-economically Important, but Potentially Short-lived, Species
• Moisture Relations of Seed Longevity (and their Limits; Orthodox Seeds)

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