Staying Ahead of SCN, Alternative Sources of Resistance
Department of Crop Sciences
Soybean cyst nematode (SCN) is a tiny worm that causes yield losses by infecting soybean roots. The pest is estimated to rob more soybean yield than any other pathogen. The use of SCN-resistant varieties is a critical part of any SCN control strategy. When SCN-resistant varieties are selected, an important consideration is the source of the SCN resistance. The most common source of SCN resistance for varieties in Illinois is PI 88788 and there are many varieties available with SCN resistance from this and other sources.
Yields of SCN-resistant varieties match those of susceptible varieties, so the purchase of SCN-resistant varieties is a good insurance policy. Our research supports this lack of yield drag associated with resistance. We found that in fields with low SCN populations, there was little, if any yield drag associated with the major SCN resistance gene from PI 88788. In fields with high SCN pressure, the SCN resistance gene resulted in a significant yield increase and kept the SCN populations from increasing during the growing season.
Although there are many SCN-resistant varieties available, there is a danger that we are too dependent on the PI 88788 source of resistance. Among maturity group II to IV varieties that have an identified source of SCN resistance, PI 88788 is the sole resistance source for 93% and is at least one of the resistance sources for 95%. If we depend too much on the PI 88788 resistance source, we run the risk of SCN populations overcoming this resistance.
Breeders realize that varieties are needed with resistance genes from new resistance sources, and they have been breeding varieties using these new sources for many years. Unfortunately, it has been difficult to combine resistance from these new sources with high yield. Progress is being made in this area and there are now high yielding varieties available to growers that have SCN resistance from PI 437654 (also known as the Hartwig or Cyst-X source). We are also working with resistance from PI 468916, a wild soybean resistance source (Glycine soja). We have identified new SCN resistance genes from this source that we are now breeding into soybean varieties. We hope that the breeding of these new resistance genes into high yielding soybean varieties will help keep resistance ahead of the nematodes, allowing profitable soybean production to continue in Illinois.