Seed Storage & Conservation
Proper storage of seed is vital to conserving its vigor
and vitality. Seeds can last from a few years to
centuries, depending on the species and the storage
conditions. In general, most seeds stored in cool, dry
conditions will survive longer than seeds stored in a
wet, warm environment. In many parts of the world,
agricultural seeds are stored in bins that are open to
the ambient conditions, often resulting in short storage
life and poor seed quality in hot, humid regions, as
well as losses due to insects and rodents. As the
viability period for seeds decreases by half for every
1% increase in seed moisture content or 10°F (~5°C)
increase in temperature, sealed bins and controlled
environments are used to maintain seed viability for
longer periods. A common rule of thumb is that the
temperature (in Fahrenheit) plus the relative humidity
in the air (in percent) should total less than 100 for
satisfactory seed storage.
At seed banks that store seeds to preserve genetic
diversity, seeds are dried to optimum moisture content,
evaluated for quality and
genetic purity
and sealed in moisture-proof containers. For short-term
storage, seeds are dried and placed in sealed containers
at 5°C. They are stored at temperatures below freezing
for long-term preservation (0°F or -20°C), including the
use of cryopreservation, or freezing in or over liquid
nitrogen at -180°C, for extremely long-term storage. But
when it comes to seed storage, one size does not fit
all. Some species have short-lived seeds that do not
tolerate dehydration and are therefore difficult to
store. Plants producing these recalcitrant seeds
must be maintained as living populations, making them
vulnerable to loss due to changes in land use or weather
patterns.
The vigor and viability of seeds stored even at low
temperatures declines over time. The continued
maintenance of specific seed lines requires that they
periodically be removed from storage and used to produce
a new crop of seeds. Seed storage facilities therefore
need not only modern storage equipment but also the
land, personnel and expertise to periodically grow the
stored seeds under conditions that maintain their
genetic diversity and purity in order to replenish the
original seed stock. Thus, core seed repositories such
as the
U.S. National Center for Genetic Resources Preservationin
Ft. Collins, Colorado, are complemented by a number of
branch stations in different growing environments to
store and replenish seed collections of diverse species.
Recalcitrant seeds |
Recalcitrant seeds
are seeds that
do not survive drying and freezing and therefore cannot
be stored for long periods of time. Some plants that
produce recalcitrant seeds include
avocado,
mango,
lychee and some horticultural trees.
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