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Agronomy Day 2009

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Tour B

Using Resistance Genes to Combat the Soybean Aphid

Brian Diers
Brian Diers
Associate Professor
Department of Crop Sciences
bdiers@illinois.edu
Carol Bonin
Carol Bonin
Graduate Research Assistant
Department of Crop Sciences
cbonin2@illinois.edu

The soybean aphid, Aphis glycines, was first identified in Wisconsin in 2001 and has quickly spread throughout the Midwestern soybean growing region.  Soybean aphids suck sap from plants, resulting in energy depletion which can dramatically reduce yields over 50% in epidemic years.  While the only current control method for soybean aphid is insecticides, soybean breeders are quickly working to develop new varieties with aphid resistance genes.

Breeders have identified four aphid resistance genes, termed “Rag” genes, and more are likely to be discovered as thousands of exotic soybean types are screened for resistance.  Research done by the University of Illinois and USDA-ARS funded by the Illinois Soybean Association and the United Soybean Board has resulted in the discovery of Rag1 and Rag2.  Limited seed of one aphid resistant variety carrying Rag1 was available to growers in 2009, and additional varieties will be available in 2010.  Field tests of Rag1 show that this gene is successful at protecting soybean yields under high aphid pressure, and work is currently being done to develop and evaluate varieties that contain Rag2.  Both the Rag1 and Rag2 genes have been licensed by major soybean breeding companies that are incorporating these genes into their varieties.

Resistance genes Rag1 and Rag2 are both single genes that effectively control soybean aphid, making it relatively straightforward to develop aphid-resistant soybean varieties.  However, this also means that it will be easier for aphids to overcome these single genes compared to plant resistance controlled by more complicated inheritance mechanisms.  Researchers have already identified aphid biotypes that can defeat Rag1 and Rag2, making it critical to continue resistance gene discovery projects.  With a little luck and a lot of hard work, researchers are hopeful to be able to provide soybean growers with reliable genetic control of the soybean aphid.

aphids

Graphs courtesy of Matt O’Neal, Department of Entomology, Iowa State University

aphid yield aphid numbers
change and challenge