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Safeguarding Canadian potatoes

Moving forward in the 21st century, genetic preservation of all crops is more and more critical. Due to aggressive and specific commercial breeding programs over the last century and the related loss of varieties of many crops, genetic diversity in both food crops and livestock has shrunk considerably.


April 6, 2009
By Top Crop Manager

Moving forward in the 21st century, genetic preservation of all crops is more and more critical. Due to aggressive and specific commercial breeding programs over the last century and the related loss of varieties of many crops, genetic diversity in both food crops and livestock has shrunk considerably.

POT-6-1--Petri-dish-contain  
AC Red Island microtubers stored in a petri dish.
POT-6-1--Propagation-box-wi
Single node cuttings being grown.
POT-6-1--In-vitro-potato-pl
The resulting potato plant with microtubers.


That is why genetic repositories such as the Plant Gene Resources of
Canada (PGRC) in Saskatoon, Saskatchewan, are so important. Dr. Ken
Richards, PGRC research manager, says the heritage potato samples it
contains “are available for use by national and international plant
breeders, plant pathologists and geneticists for crop improvement and
hence contribute to the development of new opportunities for the
Canadian agricultural system.”

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He adds “Through its conservation efforts the repository contributes to
the security, protection and safety of the Canadian food system and the
health and wellness of Canadians. The potato repository houses a
national treasure and influences our future food supply.”

While remotely located, long-term storage facilities for dormant seeds
are being developed, potatoes require different means of preservation.
For example, the new Svalbard Global Seed Vault, located in a concrete
reinforced tunnel 70 metres into the mountain on the northern Norwegian
Svalbard archipelago, provides storage for about 1400 seed genebanks
from around the world.

However, “Clonally propagated crops, like potato, cannot be preserved
in the same way as seed-propagated crops in facilities such as
Svalbard,” says Jane Percy, a research technician at Potato Gene
Resources Repository (PGRR) at Agriculture and Agri-Food Canada’s
Potato Research Centre in Fredericton, New Brunswick. “Clonal crops
require renewal and propagation on a regular basis.”

There are two main long-term storage solutions for potato. These
include cryo-conservation of potato meristems in liquid nitrogen. “The
Braunschweig potato cultivar collection in Germany, reported in 1999
that 245 cultivars were cryo-stored with a survival rate of 55 to 100
percent and a plant regeneration rate of 40 percent,” says Percy.

The second strategy, one in which PGRR plays a central role, addresses
the need for medium- to long-term remote location genetic storage
through microtuber production. Microtubers provide an efficient way to
preserve genetics because they take up less space in comparison to
whole plant propagation. They are readily produced from clones, easily
harvested, transported and stored. They retain dormancy for many
months, ensuring a back-up of the original germplasm and a source of
retrievable material in case of loss or disaster.

“This method of germplasm backup provides an efficient and reliable
strategy for the PGRR to duplicate accessions,” says Percy, “easily
transport and safely store them at a remote geographic location, and
have them available in the future, should the need arise.

Microtuber production at PGRR
PGRR has developed the following regimen for microtuber production,
which accommodates all potato clones in the bank and produces reliable
results. Most of the PGRR’s 132 potato clone collection is stored in
vitro. In other words, this material is grown in controlled environment
cabinets that maintain a constant temperature of 17-19 C, light
intensity and day-length.
 
“These in vitro clones require transfer to fresh media every eight
weeks and are always available to multiply and distribute,” says Percy.
“The repository also maintains clones at 12 C, on a slow growth medium.
This increases the time between transfers and provides a back-up to the
main collection. These regimens are considered short-term, on-site
germplasm maintenance.”

Microtuber production begins with sterile dissection of an in vitro
potato plant. The single node cuttings, each with an axillary bud and
subtending leaf, are placed into propagation boxes and stimulated to
grow using nutrients and day-length reduction. “No alterations are made
to the nitrogen levels in the medium,” says Percy. “No growth
regulators are added due to concerns about the possibility of somatic
change.”

Following a period of growth of four to six months in this environment,
the plants have begun to senesce; microtubers have formed and are ready
to be harvested. Approximately 20 microtubers of each clone are
harvested aseptically and placed into two sterile petri dishes with
damp filter paper. The dishes are then sealed and prepared for shipment
to PGRC in Saskatoon.

“Once they have arrived there,” notes Percy, “they are stored in
darkness at 4 C to extend their dormancy. Microtubers remain dormant
for many months under these conditions. When their natural dormancy is
broken, they produce shoots which can initiate new in vitro plants.”
The PGRC microtuber stocks are replenished about every 18 months.

Richard Tarn, PGRR curator, says the facility also provides in vitro
plantlets and greenhouse or field tubers for breeding, research and
heritage preservation. However, he notes, “While extensively tested for
freedom from disease, the plantlets and tubers distributed by PGRR are
produced outside the Canadian Seed Certification System and are not
eligible for Certification.”

Potatoes destined for certification under the Canadian Seed Potato
Certification System begin with tested plantlets established in vitro
in a facility accredited for this task by the Canadian Food Inspection
Agency. The plantlets are used to produce greenhouse tubers, which then
go to the field in a limited generation system, at each step meeting
strict regulatory standards.