Urbana, Illinois, USA
August 10, 2009
This year farmers in the Midwest
are growing a new variety of soybeans developed by
University of Illinois (U of
I) researchers that has resistance to soybean aphids. However,
in addition to the resistant plants, U of I researchers also
discovered a new soybean aphid which is not controlled by this
resistance.
Soybean aphids made their first appearance in North America in
the summer of 2000, resulting in tremendous crop losses for
farmers. U of I researchers began immediately searching for a
variety of soybean that is resistant to the new pest.
Dowling and Jackson were the first two resistant varieties to be
identified. “We have the U. S. Soybean Germplasm collection here
at Illinois. It houses about 18,000 different accessions,” said
Glen Hartman, soybean plant pathologist with the USDA and U of
I. “We didn’t screen all 18,000, but we went through a small set
of 4,000 to 5,000 and that’s where Jackson and Dowling came
from. We knew they were resistant, but we had to do the
crossings and look at the inheritance patterns to figure out
whether the resistance was because of a single gene or multiple
genes.”
With additional screening, a third soybean resistant to aphids
was found --a Japanese variety known as PI 200538. “After we
mapped the genes from these sources, we discovered that Jackson
and Dowling had genes mapping to the same place on a chromosome
and the PI had a gene mapping to a different place. This means
that Jackson and Dowling likely have the same resistance gene
and PI 200538 has a different gene we can use in breeding.”
Diers said that both Jackson and Dowling originated in the
southern United States, so neither could be grown to seed in the
Midwest. They used traditional breeding techniques together with
marker-assisted selection to quickly breed the resistance genes
into varieties that are adapted to the Midwest.
“Because the aphid resistance is conferred by a single gene in
the resistance sources, we were able to breed these genes into
Midwest-adapted varieties quickly and easily,” Diers said. “We
can complete three crossing generations a year by using both
greenhouses and fields. This year is a milestone because we now
have a variety that’s being commercially produced that carries
the resistance gene from Dowling. This is its first commercial
production of an aphid-resistant variety in the Midwest.”
Unfortunately, the celebration didn’t last long. While studying
soybean plants, they discovered a new type of aphid. “We were
excited about finding the resistance. We discovered this gene
from Dowling and Jackson, bred it into varieties and we ‘hoped
that we could solve the aphid problem,’ but of course things are
never that simple,” Diers said. “We found that there are
different biotypes of soybean aphids, including a biotype that
can overcome the resistance gene for Dowling.”
In tests, this new aphid was able to infest Dowling as well as
it could any susceptible genotype of soybean. “We don’t know how
widespread those aphids are or whether or not this is actually
going to occur in fields, but certainly it’s something to be
concerned about because we know that resistance isn’t going to
be perfect,” Diers said.
The good news is that the PI 200538 gene for resistance is
different than the one in Dowling and Jackson. “We found that
this second resistance gene in the PI protects the plants
against this new biotype of aphid. We are currently breeding the
PI 200538 gene into varieties, but it will be at least a few
years before any varieties with this gene will be released.”
Even after the appearance of this new aphid, Diers is still
optimistic. “We have one variety with the Dowling resistance
gene that’s being commercialized this year. A company is
increasing seed of a second variety with the Dowling gene that
should be commercialized next year. So we’ll have two varieties
available to growers.” He explained that the U of I
aphid-resistant germplasm and marker technology is licensed to
private seed companies who are using it to breed their own
varieties.”
The first aphid-resistant variety developed and released by the
University of Illinois is Round-up Ready, and the second is a
conventional, non-Round-up Ready variety. Diers says “we believe
that the aphid resistance in a conventional background will be
especially helpful to organic soybean producers because
currently if they have aphids in their fields, they don’t have
any practical method of control because they cannot spray
insecticides. I’ve been contacted by some organic growers in
northern Iowa and southern Minnesota who are ready to give up
growing organic soybeans because aphids have caused such large
losses.”
Diers said that resistant varieties can save farmers money and
help the environment. “Farmers have been controlling soybean
aphids by spraying insecticides. If we can deploy resistance,
this could reduce the use of these insecticides, which will have
many environmental benefits.”
The message to farmers is that there are going to be varieties
with soybean aphid resistance available. “The tests we’ve done
have shown that we have less aphid reproduction on these
resistant lines than on susceptible lines,” Diers said. “But so
far the resistance isn’t a magic bullet. You can’t grow these
aphid-resistant varieties and not scout for aphids because there
may be aphids in your fields that can defeat the resistance.”
The other unknown is how adaptable aphids will be to these new
varieties. “Our hope is that we can combine these two genes and
get more durable resistance,” Diers said. “We hope that we can
develop a plant with a number of resistance genes so that if any
one of them breaks down, the plant would still be resistant.”
This work was supported by funding from the United Soybean Board
and the Illinois Soybean Association. “Without funding from
these organizations, our research on aphid resistance and the
development of aphid-resistant varieties would not have been
possible,” says Diers.
The work appeared in the following journals: Soybean Aphid
Resistance Genes in the Soybean Cultivars Dowling and Jackson
Map to Linkage Group M was published in a 2007 issue of Mol
Breeding. Discovery of Soybean Aphid Biotypes was published in
the May-June 2008 issue of Crop Science. Inheritance of
Resistance to the Soybean Aphid in Soybean PI 200538 was
published in the July-August 2009 issue of Crop Science. Funding
was provided by the United Soybean Board and the Illinois
Soybean Association. Yan Li, Curtis B. Hill, Shawn R. Carlson,
Ki-Seung Kim, M.A. Rouf Mian, and Laura Crull contributed to the
research.
This research will be presented at
Agronomy Day, Thursday, August 13. Agronomy Day is an annual
event attended by over 1,000 visitors to the Crop Sciences
Research and Education Center which is located south of the U of
I main Urbana-Champaign campus off of St. Mary's Road on South
Wright Street Extended. Hour-long tours will begin at 7:00 a.m.
making stops at research plots and repeating every half-hour
until approximately noon. |
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