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Research Highlights

Research Highlights
Making advancements for Soybean Cyst Nematode through plant breeding

Smaller motile and larger root-feeding soybean cyst nematodes (stained to aid visualization), on soybean root. Photo: Bent laboratory

By Carol Brown

There are many experts working for farmers to crack the Soybean Cyst Nematode (SCN) problem, which greatly affects yields across the United States each year. And they are coming about it from all directions, from improving chemical treatments or changing management strategies to developing a more-resistant soybean plant itself.

That’s where the acclaimed team of Andrew Bent, Brian Diers, and Matthew Hudson come in. For a decade, this trio of scientists has been highly successful in their work to understand and breed soybeans with stronger SCN resistance.

Bent, a plant pathology professor at the University of Wisconsin, is currently leading a research project funded by the United Soybean Board (USB) to improve the plant’s resistance to this yield-robbing disease.  His colleagues on the project, Diers and Hudson, are soybean geneticists at the University of Illinois.

A key part of their work focuses on Rhg1, the soybean gene most responsible for resistance to SCN.

“The genetic locus called Rhg1 has been used for decades to fight SCN and it’s worked beautifully for decades,” said Bent. “But it’s working less and less well with every passing soybean season because the nematodes in each field are evolving.”

Farmers may be familiar with PI88778-source Rhg1 as this version has been bred into most of the soybean varieties available on the market.

“The PI887788 Rhg1 is gradually being defeated. It still has some impact, but on its own it’s working less well,” Bent said. “The good news is there are other versions of Rhg1. The Peking source Rhg1, if bred together with the separate Rhg4 gene, is often effective against SCN populations that are overcoming the resistance in current soybean varieties. Our research team is identifying additional Rhg1 types and getting them into the soybean breeding pipeline.”

Importantly, the team is not relying solely on Rhg1. Through years of research, Diers and his colleagues searched wild soybean accessions and accessed two other genetic loci —nicknamed 006 and 007— that are very useful in rounding out the resistance of soybeans against SCN.

“Brian has now stacked these two genes together with Rhg1 in modern soybean germplasm and has a few more genes on the way,” Bent said. “He is building a more diversified SCN resistance that saves yield the way Rhg1 used to when it worked so well on its own.”

There are a lot of genes that make small contributions to SCN resistance and bringing those genes together in single soybean varieties is a valuable approach, Bent said.

“It’s not just the breeding with what you have that can be done better,” he said. “New versions of those genes can be found in collections of cultivated and wild soybeans much more readily if you know the actual DNA that causes SCN resistance, rather than a rough genetic location.”

In 2012, the Bent, Hudson, and Diers team published a landmark paper in the journal Science that defined the structure of the Rhg1 gene. It is a complex locus with variable numbers of repeat copies of three genes, each of which contributes valuable SCN resistance. This has opened multiple leads on discovering improved Rhg1 loci, one of goals of their present USB-funded project.

Some of those leads to improve Rhg1 involve genetic engineering to create new genetically modified (GM) traits, which is expensive and controversial in some places around the globe. It takes a billion-dollar-per-year trait like SCN resistance to make the investment worth considering, Bent said.

The team also is taking two non-GM approaches: traditional plant breeding with the newly discovered Rhg1 gene variants, and the use of CRISPR1 to generate targeted new variants. Minor CRISPR-guided editing of existing soybean genes is considered non-GM in the United States and some international locations.

Next steps

The team plans to continue their work developing novel SCN resistance genes that could be beneficial in commercial varieties.

“Learning the details about Rhg1 is allowing us to work out some of the resistance mechanisms. It gives us ideas about how to find improved naturally occurring versions of Rhg1, or to use CRISPR or genetic engineering to tweak the traits and make them stronger,” Bent said. “There’s evidence that although the nematodes are overcoming PI887788 Rhg1, they are still susceptible to other versions of Rhg1, which gives us all hope.”

They also are working to pinpoint the 006 and 007 genes and create molecular markers for them, which together with their new SCN resistance gene stacks, can be shared with commercial companies. This will ensure that new soybean varieties developed for other improvements, such as increased protein or high-quality oil, will have the stronger SCN resistance already built in.

“Plant breeding is a long-term undertaking,” Bent said. “Modern science has enabled all kinds of things in plant breeding that were impossible 10 years ago. We need to keep the SCN resistance pipeline primed with new genes and new knowledge.”

1CRISPR: Clustered Regularly Interspaced Short Palindromic Repeats

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