![Photo: Soybean leaves showing signs of soybean rust.](https://webarchive.library.unt.edu/web/20090509202017im_/http://www.ars.usda.gov/is/pr/2009/rust090326.jpg)
Scientists from the Agricultural Research Service,
Iowa State University and Brazil have identified a cluster of soybean genes
that provide resistance to the fungus Phakopsora pachyrhizi, which
causes Asian soybean rust. Photo courtesy of Reid Frederick, ARS
|
![For further reading](https://webarchive.library.unt.edu/web/20090509202017im_/http://www.ars.usda.gov/is/graphics/For-further-reading.gif)
|
Scientists Identify Rust Resistance Genes in
Soybeans
By Jan Suszkiw
March 26, 2009 Using state-of-the-art genomics
techniques, a team of scientists from the Agricultural Research Service (ARS),
Iowa State University (ISU) and Brazil
have identified a cluster of soybean genes that provide resistance to the
fungus Phakopsora pachyrhizi, which causes Asian soybean rust
(ASR). The discovery will help defend the $27 billion U.S. soybean crop
against ASR, through conventional breeding or biotechnological means.
ASR was first detected in the continental United States in 2004.
Although fungicide use is effective against ASR, providing farmers with
resistant cultivars is more sustainable, according to geneticist
Michelle
Graham. She's with the
ARS
Corn Insects and Crop Genetics Research Unit in Ames, Iowa.
Genetic mapping previously linked ASR resistance to five DNA regions, or
"loci," within the soybean genome, named Rpp1 through
Rpp5. Screening of 15,000 accessions in the ARS soybean germplasm
collection revealed how uncommon resistance is: Less than 5 percent of the
accessions are resistant.
Grahams group sequenced the Rpp4 locus and identified a cluster
of candidate genes that confer ASR resistance. Comparisons of susceptible and
resistant cultivars identified a single candidate gene, Rpp4C4, thought
to bestow resistance. Rpp4C4 is one of five nearly identical genes in
the Rpp4 locus. Frequent "shuffling" or recombination within
the cluster allowed new disease resistance genes to be formed.
For example, soybean cultivar Williams82 has three resistance genes in the
cluster and lacks Rpp4C4, making it vulnerable to ASR. However, line
PI459025B, the source of Rpp4 resistance, has five candidate genes.
Virus-induced gene silencing" studies were used to turn off the
Rpp4 candidate genes in PI459025B, making it susceptible to ASR and
confirming the genes importance.
Graham, together with Jenelle Meyer,
Kerry
Pedley and
Randy
Shoemaker of ARS; Chunling Yang, Chunquan Zhang, Martijn van de Mortel,
John Hill and Steve Whitham of ISU; and Ricardo Abdelnoor and Danielle Silva of
the Brazilian Agricultural Research
Corporation (Embrapa) in Brazil, published their findings recently in the
online edition of Plant
Physiology.
ARS is the principal intramural scientific research agency of the
U.S. Department of Agriculture.