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Research Highlights

Research Highlights
An integrated approach to enhance durability of SCN resistance for long-term strategic SCN management

By Julie Meyer, Lead PI: Melissa Mitchum (University of Missouri)

Over 95% of the soybean varieties currently marketed in the north-central United States have PI 88788 as the source of  resistance to soybean cyst nematode (SCN).  The effectiveness of PI 88788 resistance has decreased over time, leaving producers with limited options for rotation once virulent nematode populations develop in their field. 

Many other sources of resistance have been identified over the past two decades, but these genes have largely have not been transferred into varieties.

With checkoff funding provided by the North Central Soybean Research Program, a multi-state,  interdisciplinary team of researchers are working to increase the genetic diversity of SCN resistance in commercially-available SCN-resistant soybean cultivars. Soybean nematologists on the team are determining the most effective rotation practices that preserve these sources of resistance.

Stacking SCN resistance genes for durable resistance

Promising resistance genes include Rhg1 from PI88788 or PI437654 (Hartwig), Rhg4 from PI437654, genes from wild soybean G. soja, a gene from PI437654, and several genes from PI567516C. Over 200 experimental lines have been developed with new combinations of these resistance genes. Plant breeders and other scientists worldwide can access this information through “SCNBase.org”, an online portal which displays all the relevant genetic information in a user-friendly manner.

Testing is done in  SCN-infested and non-infested environments to determine whether any of the genes are associated with yield drag.  Gene combinations that are effective in controlling SCN, and are not associated with negative yield, are being bred into elite soybean germplasm. The team has already produced one commercialized soybean variety that has the Rhg1 gene combined with the two resistance genes from Glycine soja.

Different SCN resistance gene stacks are tested in different field locations to gauge their influence on the nematodes’ ability to overcome soybean resistance genes.  This is a critical step to ensure the longevity of the varieties.

The  project also coordinates the regional multi-site testing of publicly-developed SCN resistant soybean lines.  The results from the tests are used by plant breeders to improve their efforts and provide farmers with the information they need to make informed variety selections.  

The number of gene repeats matters

 A significant outcome of this research is the discovery that SCN resistance genes are repeated at particular places on the genome, and that more copies means greater resistance levels. Beause the number of gene repeats can be determined by a simple and accurate molecular test, this advance is speeding up breeding progress significantly.

It also explains why some SCN-resistant varieties with PI 88788 resistance are more effective than others: they have higher copy numbers of those genes.

A new understanding of how nematodes adapt to resistant cultivars

Another milestone from the project is a new understanding about genes in the nematode that allow for adaptation to resistant cultivars.  The research  has identified a whole suit of previously undiscovered “effectors” — the nematode-secreted proteins that play critical roles in establishing infection. The team is conducting in-depth studies on the role of these effectors, paving the way to the development of new nematode resistance resources in the future.

Details about this project can be found on the USB National Soybean Checkoff Research Database at  https://www.soybeanresearchdata.com/Project.aspx?id=52996

Resources

Soybean resistance to the soybean cyst nematode Heterodera glycines: an update. M. Mitchum, Phytopathology 2016

Pyramiding of alleles from multiple sources increases the resistance of soybean to highly virulent soybean cyst nematode isolates. Summary in Crop Science, 2017.

ISU scientists overcome repetitive DNA to sequence the genome of devastating soybean pest, 2019

To find research related to this Research Highlight, please visit the National Soybean Checkoff Research Database.