For the limited number of species studied, the storage characteristics oforchid seeds are
classified as 'orthodox' in the sense that seed longevity is enhanced by reducing moisture contents (from
around 20%, wet basis, to 5%) and decreasing storage temperatures (from 62°C to O°C). When stored dry
at 5-8°C, the time taken for viability to fall to 50% can be 8-14 years, (assuming high initial seed quality).
However, seeds ofCattleya aurantiaca exhibit reduced longevity at 5°C when stored at equilibrium moisture
contents both above and below 5%, indicating that the optimal water status for these seeds during storage
is approximately 30% Lh. (or a water potential of ca. -150 MPa). C. aurantiaca seeds at 2.2 to 5.6%
moisture content (up to 31 % Lh.) generally exhibit reduced longevity at -18°C compared to 5°C, and this
sensitivity to sub-zero storage has been shown by differential scanning calorimetry to coincide with the
presence of the seed lipids in a transitional conformation state. Similar results in the literature for 'dry'
seeds of other tropical orchids stored at - 10°C suggest that the long-term conservation of such species
under conventional seed bank conditions (i.e., about -20°C and 5% moisture content) is problematical.
In contrast, dry seeds oftwo temperate species DactylorhizaJuschii and Orchis moria germinated after 6-
7 yr storage ofsub-zero temperatures. The results are discussed in relation to seed longevity in species from
other plant families.
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