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After nearly three years of effort, a
team of researchers at the U of I has identified a single-gene
source of aphid resistance that can be easily crossed into elite
commercial varieties.
The lead scientists in this effort are
Glen Hartman, plant pathologist with the USDA's Agricultural
Research Service at the U of I; Curtis Hill, senior research
associate; and Brian Diers, soybean breeder from the U of I's
Department of Crops Sciences. Funding for the research has been
provided by the Illinois Soybean Checkoff Board.
"This gene has been tested in both the
greenhouse and the field and has consistently prevented colonization
by soybean aphids," Hartman said. "Because it is a single dominant
gene with identified DNA markers, it can be readily introduced into
susceptible commercial soybean varieties by backcrossing, using
marker-assisted selection."
The methods for breeding plants with
the aphid-resistance gene will be licensed for use in both public
and private breeding programs.
"Growers could have resistant varieties
fairly quickly, especially if industry adopts this technology,"
Hartman said. "I think three to four years would be a reasonable
time frame for that to happen."
The aphids were first discovered in
large numbers in fields near the end of the 2000 growing season.
After careful scientific investigation, they were identified as
Aphis glycines, which had previously been reported only in Asia,
Australia and some Pacific islands. By 2003, this pest had emerged
as a major problem for growers throughout the Midwest.
"When the aphids infest a field, the
most common means of control is to spray the field with an
insecticide that can cost as much as 20 to 25 dollars per acre,"
Hartman said. "In 2003 alone, more than 1 million acres were sprayed
in Illinois and more than 3 million acres in both Iowa and
Minnesota. Once resistant commercial varieties are available, the
savings to growers will be substantial."
As part of the initial screening
process, the team evaluated the various commercial soybean varieties
that had been submitted to the yield trials at U of I for resistance
to the aphids.
"After screening more than 700
varieties, we found that all of them were basically susceptible to
this pest," Hartman said. "We also determined that there had not
been any reported resistance from the germplasm screened in the part
of the world where the aphids originated, which is China."
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In the next step, they began screening
about 100 cultivars that had been identified as the major genetic
contributors to modern soybean varieties. Those ancestral lines
account for more than 90 percent of the genetic variation in our
current soybeans.
"Luckily we found resistance in two
different cultivars," Hill said. "One is called Jackson, which is an
old Southern cultivar. Another was Dowling, which also is an old
variety grown in the South."
As part of the experimental design, the
resistant cultivars were tested in a specially designed field cage
with several commercial varieties and were treated with an
insecticide or left untreated.
"Even with a large numbers of aphids
present, we found virtually no difference in yield and agronomic
traits whether these resistant lines were treated with an
insecticide or not," Hartman said. "At the same time, the commercial
varieties were severely damaged when they were not treated with an
insecticide, with many of the plants actually dying."
The researchers followed up with a
series of laboratory and fields studies that identified the single
dominant gene that carried resistance to the aphids. They also
developed methods for identifying and breeding resistant plants
using marker-assisted selection.
"We were able to identify the specific
region of the chromosome where the gene is located, using genetic
markers," Diers said. "Our team also confirmed that the resistance
is conferred by a single major gene. We are now using that marker
information to breed the resistance gene into adapted soybean
varieties and testing whether there is any associated yield or
agronomic drag associated with the gene. We hope to have resistant
varieties available to farmers by 2008."
With assistance from the Office of
Technology Management at the U of I, the team has also applied for a
patent and will soon be licensing this new technology to both
university and industry breeders.
"The idea of licensing is to make it a
fair playing field for everyone," Hartman said. "Otherwise an
individual company could take this research and patent the gene for
itself. By licensing the technology to a large number of companies
and public breeders, we can ensure that the benefits will reach
growers across the Midwest as quickly and cheaply as possible."
Additional
details on this technology are available on the Internet at
http://www.otm.uiuc.edu/
techs/techdetail.asp?id=267.
[University
of Illinois news release]
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