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Breeding for Resistance to Soybean Cyst Nematodes

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

Soybean cyst nematode (SCN) continues to be the most important soybean disease in Illinois and throughout the United States. It is controlled primarily through rotating with nonhost crops and planting resistant cultivars. The development of SCN-resistant cultivars has been an important success for breeders and nematologists. These varieties have allowed soybean production to continue in many parts of the country where nematode numbers have reached levels that are too high for profitable soybean production to occur without resistance.

Figure 1. White females on soybean roots.

The development of SCN-resistant varieties began back in the 1950s, shortly after SCN was discovered in the U.S. This breeding started by screening the collection of plant introductions (PIs) to identify those with resistance to SCN. Once resistant PIs were identified, they were crossed with proven U.S. varieties and, over time, resistant varieties with high yield were developed.

Most SCN-resistant varieties available in Illinois have their resistance derived from PI 88788. The seed of PI 88788 was collected in China during 1930. The primary reason why PI 88788 is such an important source of resistance is that it has produced varieties with higher yield than has other sources. In fact, many important varieties with PI 88788 resistance were developed at the University of Illinois. These include the varieties Fayette and Jack, which can be found in the pedigree of most private and public SCN-resistant varieties in Illinois.

Figure 2. Comparison of an SCN-resistant line and an
SCN-susceptible line in a nematode-infested field.

In most fields in the state, soybean cyst nematodes currently are controlled with the PI 88788 source of resistance. However, research has shown that nematode populations in fields can evolve and eventually overcome resistance genes. For example, PI 88788 provides resistance to SCN Races 3 and 14 but only partial resistance to Race 1. In some fields where the PI 88788 source has been used extensively, SCN Race 1 is becoming more common. The evolving nature of SCN highlights the importance of developing varieties with new resistance genes.

Recent research at the University of Illinois has uncovered new resistance genes in species related to soybean. Researchers are now working to move these genes into elite soybean germplasm. These studies, along with research at other institutions, are important to insure that soybean growers in Illinois will continue to profitably grow soybeans in the presence of SCN.

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