Cambridge International A Level Biology Revision Guide

Cambridge International A Level Biology
450
The Svalbard Global Seed Vault is a seed bank run by
the government of Norway. The vault is at the end of a
120 metre tunnel cut into the rock of a mountain on the
island of Spitsbergen, within the Arctic Circle. The vault
is thought to have ideal storage conditions, and it is only
opened in winter when the environmental temperature
falls close to the operating temperature of −18 °C. Its first
seed samples went into storage in January 2008, and by
2013 the vault held over 770 000 different seed samples of
crop varieties from all over the world.
National and international organisations collect and
store seeds so that the genetic diversity in our crop plants
is not lost. Seeds from each sample are stored in the vault
at Svalbard. If seeds stored elsewhere are lost for any
reason, such as an environmental disaster that destroys
a seed bank, then there will always be duplicate samples
available from Svalbard. Such problems could range from
mismanagement or loss of funding to accidents or failure
of equipment. The depositing seed bank owns its seeds
and alone has access to them. Any research organisation
wishing to use any of the seeds has to apply to the original
seed bank for such seeds. The storage of the seeds is free of
charge, as the costs of the upkeep of the vault are covered
by the Norwegian government and by the Global Crop
Diversity Trust. This trust also helps developing countries
to select and package seeds that can then be sent to
Svalbard to be stored.
Another important seed bank is that of the International
Rice Institute in the Philippines, which holds all rice varieties.
Many plants produce seeds, known as orthodox seeds,
that remain viable for at least 15 years if they are carefully
dehydrated until they contain only about 5% water, and
then stored at around −15 to −20 °C. With this small water
content, there is little danger that cells in the seed will be
damaged by ice crystals during freezing and thawing.
The only way to find out whether or not stored seeds
are still viable is to try to germinate them. Seed banks
carry out germination tests at five-year intervals. When
fewer than 85% of the seeds germinate successfully, then
plants are grown from these seeds so that fresh seed can be
collected and stored.
When such plants are grown from samples of stored
seed, there is the possibility of altering the genetic diversity
that was originally stored. Small samples of seeds from
rare plants present a particular problem, as even smaller
samples of the original are taken to test for viability or
to grow into plants to increase the number of seeds in
store. Such samples are unlikely to contain all the genetic
diversity of the original sample. The only answer to this
problem is to put as large and diverse a sample as possible
into store in the first place.
Most seeds are easy to store, but some plants have seeds
that cannot be dried and frozen. These ʻrecalcitrant seedsʼ,
as they are called, include seeds of economically important
tropical species, such as rubber, coconut palm, coffee and
cocoa (Figure 18.35). The only ways to keep the genetic
diversity of these species are to collect seeds and grow
successive generations of plants or to keep them as tissue
culture. Cocoa is banked as trees. The International Cocoa
Genebank in Trinidad has about 12 000 trees – examples
of all the cocoa varieties found in Latin America and the
Caribbean. Selected material from the Trinidad collection
is distributed to other cocoa-producing countries after it
has been through quarantine at the University of Reading
in the UK.
Coconut palms are particularly difficult to bank
(Figure 18.36). The seed (the coconut) is very large, and
the embryo is too large to freeze successfully. Collectors
remove the embryos from the seeds, culture them in sterile
tubes and eventually plant them.
Figure 18.35 The future of cocoa, Theobroma cacao, is
threatened by diseases, climate change, natural disasters,
limited genetic diversity and the failure to manage plantations
by replacing old trees. 30–40% of the world’s production is
lost to pests and disease.