Planting soybean cyst nematode (SCN) varieties is one of the most effective tactics for managing the most important pathogen of soybeans. However, SCN-resistant varieties are not all created equal. You should consider the following characteristics when selecting SCN resistant varieties for your fields:
- SCN population suppression
- Genetic source of SCN resistance
- Tolerance to sudden death syndrome (SDS)
Yield is the most important characteristic to look for when selecting SCN-resistant varieties. Look for yield performance data collected from SCN infested fields or plots.
Next, consider the ability of the SCN-resistant varieties to inhibit SCN reproduction in infested fields or greenhouse trials. Reducing SCN population densities is essential to improving long-term soybean yields and SCN-resistant varieties vary widely in their abilities to do it. The reproductive index is commonly used to measure and report the SCN population suppression effects of resistant varieties. The reproductive index is calculated by dividing the number of nematodes at harvest by the number of nematodes collected at planting. A reproductive index of less than one means that the SCN population was reduced.
It is also important to know the genetic source of the SCN-resistance in the varieties you plan to plant. There are three genetic sources of resistance in commercial soybean varieties: PI88788, PI548402 (Peking) and PI437654 (CystX or Hartwig). If the same source of resistance is used in a field for many years, the SCN population will shift and become able to reproduce and cause significant yield losses on varieties containing this source of resistance. This situation can be prevented by planting varieties with different sources of resistance. This is not easy as nearly 95% of the SCN-resistant varieties contain the PI88788 source of resistance.
If you cannot rotate to a different source of resistance, you should rotate to a different soybean variety. Recent research from Missouri and Illinois indicates that this will be helpful in preventing SCN population shifts.
If you have planted SCN-resistant varieties and your yields have been declining or are lower than expected, the SCN population may have shifted and overcome the source of resistance you have been using. Michigan State University offers a mini HG Type test that measures the ability of the SCN population in your soil to reproduce on the three commercially available sources of SCN-resistance. Information on SCN type testing is available online at the MSU Diagnostic Services website.
If the population reproduces on varieties with Peking resistance, the SCN population is HG type 1. If SCN reproduction occurs on PI88788, the population is HG type 2. And if the SCN population reproduces on CystX or Hartwig, the population is a HG type 4. If the population can reproduce on more than one source of resistance, the types are listed and separated by periods.
The final characteristic to consider is disease tolerance or resistance. Because there is a relationship between SCN and SDS, you should also consider the SDS-tolerance of the SCN-resistant varieties. Please see the Michigan State University Extension article, “Sources of information for selecting soybean cyst nematode-resistant varieties,” for more information.