How should the SCN-resistant varieties be used?
Fig. 13. Average yield of top ten SCN-resistant varieties (R) and top ten susceptible varieties (S) in SCN-infested and non-infested fields in 1999-2002.
Many SCN-resistant varieties in Maturity Groups II and I and a few in Maturity Group 0 have been developed and are available for Minnesota soybean producers. Performance of a resistant variety in an SCN-infested field depends on the genetics of both the soybean and the nematode.
In the past, resistant varieties produced 5-10% less yield than susceptible varieties when both were grown in the absence of the nematode (Fig. 13). Although current elite, high-yielding susceptible varieties may still outperform current resistant varieties in fields where there are no soybean cyst nematodes or fewer than 200 eggs/100cc of soil, the yield potential of resistant varieties has been improved, and some elite resistant varieties have fairly high yield.
Most (~95%) SCN-resistant varieties are developed from the single source of resistance PI 88788, and a few from Peking and PI 437654. Repeated use of the same resistant variety or continuous use of varieties with the same resistance source may eventually lead to SCN populations that can overcome resistance from the common source. Consequently, soybean varieties with resistance genes from different sources should be alternated to slow changes in HG Type composition and increase effectiveness of resistant varieties.
Table 4. Determine whether an SCN-resistant variety can be used in a field based on the source and level of resistance of the variety and HG Type of SCN population in the field.
|FI of HG Type 0 on a variety (Variety resistance)||FI of SCN from the field on the source of resistance of the variety (HG Type)|
|< 10||10-30||> 30|
|< 10||Low risk||Moderate risk||High risk|
|10-30||Moderate risk||High risk||Very high risk|
|> 30||High risk||Very high risk||Very high risk|
If resistant varieties have been used in a field for a number of (>5) years, the HG Type should be determined to make sure the varieties are still resistant to the population. Different commercial SCN-resistant varieties have different levels of resistance (Fig. 14). Check data of the varieties tested in the greenhouse and local fields, and make sure the variety you will use has a sufficient level of resistance to the SCN population in your field.
Fig. 14. Levels of resistance to HG Type 0 of commercial soybean varieties labeled as SCN-resistant in 2010.
Not all the varieties labeled as SCN-resistant are resistant (Fig. 14). Data on SCN resistance and yield potential is available as part of the University of Minnesota Soybean Breeding Project's contribution to the annual publication titled "Minnesota Variety Trials Results." Information about yield potential and reproduction of SCN population on individual soybean varieties is also available at soybeans.umn.edu and at the University of Minnesota Southern Research and Outreach Center website at sroc.cfans.umn.edu.
Table 4 offers guidance for selecting varieties to manage SCN based on resistant level of a variety and HG Type of SCN from the field. Yield potential is certainly the most important criterion in variety selection.