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Breeding Soybeans for Resistance to SDS

Brian Diers Brian Diers
Associate Professor
Department of Crop Sciences
(217) 265-4062; bdiers@illinois.edu
  Wayne Pederson Wayne Pederson
Associate Professor
Department of Crop Sciences
(217) 333-3847; wpederse@illinois.edu

Sudden death syndrome (SDS) in soybean is estimated to be the second most costly soybean disease in Illinois. In the year 2000, yield losses in Illinois were estimated at $400 million.Genetic resistance is the most viable option for controlling this disease. Although no varieties have been identified with complete resistance to the disease, partial resistance is available in some varieties. These partially resistant varieties will have fewer disease symptoms and less yield losses than other varieties that are highly susceptible to the disease. Information on the level of resistance of varieties is available from a number of sources, including seed company representatives and the Varietal Information Program for Soybeans (VIPS), which can be accessed at http://www.vipsoybeans.org/.

The development of high-yield varieties with SDS resistance has been slow due to a number of factors. One factor is the difficulty in obtaining consistent disease symptoms in field tests. Because the disease is dependent on weather conditions, it's often difficult to obtain good disease symptoms in the field when you want them. A second factor is the lack of sources of complete resistance. Experiments have shown that the genetics of resistance to SDS is complex, with many genes needed to give partial resistance. Breeders and pathologists are now exploring plant introductions, which are soybean varieties collected throughout the world, as new sources of resistance. These plant introductions could provide new resistance genes that enhance the level of resistance currently available in cultivars.

Leaf symptoms of SDS
Figure 1. Leaf symptoms of SDS on a
susceptible soybean variety.

While the environment (especially wet spring weather) and resistance level of the soybean variety are the two most important factors for SDS, soil compaction appears to increase SDS. In soils with compaction or in soils with poor drainage, deep tillage down to 12 to 14 inches appears to reduce disease. In fields with little compaction, tillage appears to have little effect on SDS. We are continuing to study alternative management systems to control SDS. We also have evaluated numerous fungicide seed treatments and biological control agents, but none appear to control SDS. Therefore, the development of varieties with genetic resistance is critical to the control of SDS.

In addition to breeding for disease resistance, we are also evaluating several isolates of Fusarium solani glycines, the fungus that causes SDS, from several locations to determine the level of genetic variability. It often difficult is important to know if a source of resistance is effective against all isolates or only a few isolates. We are also evaluating several means of inoculating field plots to ensure infection in a screening nursery.

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Department of Crop Sciences
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