El Batán, Mexico
October 31, 2007
Using maize seeds instead of
leaves to determine the genetic makeup of maize, a new method
being applied by CIMMYT,
could greatly speed breeding programs, helping get
drought-tolerant or high-yielding varieties to farmers faster
and more cheaply.
Scientists use molecular markers—DNA signposts for genes that
control traits of interest, like disease resistance—to look for
genes in crop materials and select for them during breeding. Up
to now this process has been “after the fact.” Scientists grow
large numbers of plants, of which only a limited number will
contain the desired genes, and check for those genes by using
genetic information from leaf samples.
With the traditional method of using leaves to obtain DNA
samples from maize, breeders had to label plants in the field,
wait for them to grow, and analyse many leaf samples in the lab.
The researchers were tied to the fields and to the seasons, and
had to trace the samples they wanted back to source plants.
With the new method, researchers use seed tissue to find the
plants with the genes of interest. “Maize seeds are large, and
we take only a small sample that doesn’t damage the seed’s
embryo,” says Yunbi Xu,
CIMMYT maize molecular breeder. In this way, breeders will sow
only the seeds of plants with the desired traits in their
experiments. “Before, if you planted 1,000 plants, only 10 might
be useful. Now, we know what seeds to plant ahead of time,” says
Xu. By sowing only the seeds of plants with the desired
characteristics for their experiments, breeders gain an entire
growing season and save money.
Working with seeds instead of leaves can make DNA analyses up to
six times faster, which enables breeders to look at more genes
in more plant lines. “We can extract the DNA from 600 seeds in
the time it would take to do 100 DNA extractions from leaves, if
we take into account time for harvesting samples from the field
and tracking samples between the field and lab,” says Xu.
Xu and his team remove a small piece of endosperm (the tissue
surrounding the embryo) from one seed at a time—this way seeds
can still grow after the extraction. “Obtaining genetic
information from seeds could become a much faster and more
effective way of running the marker-assisted maize breeding
program,” says Xu.
Scientists extracted DNA from individual seeds from as far back
as 1993, but CIMMYT has been able to do this on a much larger
scale than before.
Collaboration with other centers
The seed extraction approach facilitates collaboration with
other research institutes in other countries, as seed fragments
(instead of the whole seeds or leaves) can be shipped easily. As
part of a workshop next October, CIMMYT will teach crop
scientists how to obtain DNA from seeds so they can bring this
technology home with them.
Breeders of other crops such as wheat, rice, and most beans may
be able to use seeds to extract DNA, provided the seeds are big
enough, says Xu. |
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