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August, 2008
Source:
CIMMYT E-News, vol 5 no. 8, August 2008
 Seed
is the lifeblood of CIMMYT
research and partnerships. Behind the scenes at CIMMYT, many
thousands of seeds are on the move. Constantly arriving and
departing as seed is shared with partners, they may journey
through rigorous health testing in the laboratory, planting in
the soils of the center’s research stations, or storage in the
icy vaults of the germplasm bank.
No man is an island, and CIMMYT,
as the world center for maize and wheat research, certainly
isn’t. The center’s lifeblood is genetic variability: it is
preserved in the germplasm bank; useful genes derived from it
are incorporated in new varieties and shared with partners.
These genes come packaged up in seeds, and countless seeds enter
and leave CIMMYT every year, traveling to and from far-flung
destinations including breeding programs of national
agricultural research systems and private seed companies,
CIMMYT’s global network of offices, and its research stations
within Mexico.
Seed arriving at CIMMYT-Mexico must pass through strict testing
procedures in the Seed Health Laboratory (SHL), part of the Seed
Inspection and Distribution Unit (SIDU). “For Mexico we
represent a risk—we’re unique in importing seed from all over
the world,” says Monica Mezzalama, seed health and plant
pathologist in charge of the SHL. “We have a duty towards Mexico
and our collaborators in other countries to make sure we are not
distributing seed with diseases. It’s also important for seed
quality—we send people our best material."
Staff in the SHL test seed for insects, weeds, fungi, bacteria,
and viruses (see photo slideshow). The lab routinely checks for
pathogens under quarantine for Mexico and for partner countries.
Seed that gets a clean bill of health—a “seed release”—moves on,
often going to a breeder, whereby its potentially useful traits
may enter improved varieties. Alternatively, it may be headed
for another lab and more testing by scientists working on seed
quality or micronutrient content. Finally, many seed samples are
destined for storage in the seed bank.
Entering the vaults
On behalf of humankind, present and future, CIMMYT holds
enormous collections of seed of wheat and maize, as well as of
the crops' wild and cultivated relatives. For Tom Payne, head of
the wheat germplasm bank (seed bank), the focus is on useful
diversity, particularly from materials that have already
undergone some breeding. “The most valuable germplasm (genetic
material or seeds) is the germplasm we know the most about. It
lets you look for the traits you’re interested in,” he says.
Nonetheless, Payne says that breeders also recognize the value
of landraces—traditional farmer varieties—and wild relatives:
“When Ug99 (a new, highly-virulent form of stem rust) broke out
in Africa, we sent 4,000 randomly-selected landraces for
screening and found new sources of resistance.”
In the case of wheat, once cleared by the SHL, seed of new
samples for the germplasm bank goes into several packets with
different destinations. At least 200 grams will enter the
"active" collection, from which external requests for seed are
met. Additional packets are prepared for long-term storage at
CIMMYT and, finally, three partner banks as back-ups. Because
the center normally receives small amounts of seed, it has to be
grown out, or "multiplied," to harvest enough for research,
storage, and back-up purposes. Seed is also multiplied for
distribution. Again, quarantine precautions require that new
wheat seed first be grown at the center’s headquarters and then
vetted by the SHL, after which it travels 2,500 kilometers north
to be re-sown at a Mexican desert location certified as free
from the diseases. The final product is shipped back to CIMMYT
headquarters and once more inspected by the SHL.
Regenerating germplasm bank collections
Eventually seed in the germplasm bank ages and begins to lose
its ability to germinate. Also, supplies of frequently-requested
samples eventually run short. When either occurs, viable seed
from the sample is sown to replenish the collection—a process
known as "regeneration." "In 2008, the germplasm bank
regenerated a record 18,000 wheat lines," says Bibiana Espinosa,
the principal research assistant who manages CIMMYT’s wheat
germplasm collection. "That's 45% more than in typical years."
Pollen from a single maize plant can fertilize seed of many
neighboring plants, so regeneration of maize seed is more costly
and complex than for wheat plants, which are self-fertilizing.
Maize crosses must be carefully mapped out and controlled to
ensure that the diversity from the original sample is as closely
replicated as possible. “Regenerating and storing one sample of
maize costs around USD 250 or more—maybe 20 times more than a
sample of wheat,” says Payne. “On a single hectare of land you
can regenerate thousands of wheat lines, but because individual
maize populations or landraces may embody tremendous genetic
diversity, they require far more space to regenerate properly.”
Keeping track of hundreds of thousands of seed collections poses
a serious challenge for germplasm bank staff. CIMMYT has
recently begun marking seed packets with a barcode linked to
crop database systems for physical and molecular traits. “The
goal is to internet-enable all these databases and link to
specific seed collections in the bank, helping people make
selections,” says Payne.
Seed collections and genetically modified crops
“CIMMYT's internal policy is to avoid the involuntary presence
of transgenes in its germplasm," says Mezzalama, referring to
genes from other species that are introduced into crop plants
like maize using genetic engineering. This means strict
monitoring of maize seed that the center introduces from abroad,
either for storage in the bank or for breeding purposes. As a
further measure, regeneration plantings are surrounded by
“sentinel plots” from which seed is harvested and tested in the
laboratory to check for the possible arrival of foreign pollen.
On the road again
All seed in the germplasm bank has been certified as clean by
the SHL, so it is always ready to be planted in the field or
sent to anyone who requests it. However, like any traveler, it
must carry a passport—an international phytosanitary
certificate—to move between countries. In addition, CIMMYT seed
travels only if prospective recipients accept the "Standard
Material Transfer Agreement"—which stipulates among other things
that the seed may not be sold or patented, and was adopted in
the first session of the Governing Body of the International
Treaty on Plant Genetic Resources for Food and Agriculture.
Every year, SIDU receives hundreds
of requests for samples of bank or breeding seed. CIMMYT also
ships annual international nurseries (for wheat) and
international trials (for maize). These are collections of the
center's best materials, grouped into sets for specific aims:
high yield, heat tolerance, disease resistance, to name a few.
Partners request sets, grow out and evaluate the experimental
seed, and return data on the results to CIMMYT. The center
collates and analyzes the data from all sources, publishes and
distributes the results to partners, and uses the information to
guide subsequent breeding efforts. Partners who grow the trials
may keep and use seed of the varieties that interest them, or
request additional seed.
Efrén Rodríguez, who is responsible for seed distribution,
estimates that public research organizations make up around
two-thirds of CIMMYT seed recipients; the rest are private
sector seed companies. “In many countries requests from small
seed companies are increasing as the sector grows, for example
in Mexico and India,” he says. In wheat, 70–80% of requests are
for international nursery material, whereas in maize about 70%
are requests for materials from the germplasm bank. “We have
around 500 CIMMYT inbred maize lines, and all the seed companies
want a sample of these lines to use in their breeding programs,”
says Rodríguez. His team can count partners in around 150
countries, and in a year meets around 800 requests for seed.
Most of this work by SIDU and the germplasm bank goes unnoticed
by the casual visitor, but, says Mezzalama, “…the daily contact
with people around the world who really need CIMMYT seed makes
me feel very confident that I’m doing something valuable.” |
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