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Research Highlights

Research Highlights
Stacking Genes for Better Combined SCN and SDS Resistance

By Barb Baylor Anderson

U.S. soybean farmers are well-aware of the economic loss that can come from soybean cyst nematode (SCN) and sudden death syndrome (SDS). Soybean farmers suffer an average annual yield loss of close to $2 billion. The Iowa Soybean Association is funding research to reduce the yield loss created by both SCN and SDS through novel disease resistant cultivar development.

“Total U.S. soybean yield suppression from SDS and SCN together is approximately five percent of total yield. If we can reduce incidence by 20 percent through cultivation of novel SDS and SCN resistant cultivars, we can expect to see a one percent increase in soybean yield. That translates into thousands of dollars to individual farmers,” says Madan Bhattacharyya, Iowa State University agronomist and principle investigator for the checkoff-funded work.

Bhattacharyya says growing disease-resistant soybean cultivars has been the main method of controlling SCN and SDS in the past. However, the number of SCN resistance genes is limited. More diverse SCN resistance mechanisms to place into single cultivars is becoming more crucial. Meanwhile, SDS resistance is partial and encoded by more than 80 genetic loci that each contribute small effects. That makes soybean breeding for SDS resistance very time-consuming.

Such challenges led to Bhattacharyya’s interest in discovering four plant genes in transgenic soybean lines that enhance both SDS and SCN resistance. Each uses a unique mechanism to govern its resistance. The research team believes that once they establish the four novel genes together, they can reduce the extent of SCN and SDS problems. Stacking the four genes with other key genes in commercial cultivars will help generate robust disease resistance.

Stacking of soybean GmDR1 and Arabidopsis Pss30 genes enhanced SCN resistance in transgenic soybean lines.  A) Overexpression of the Arabidopsis Pss30 gene reduced the number and size of SCN cysts in roots of transgenic soybean plants. Arrows are used to show the SCN cysts. B) Stacking of soybean GmDR1 and Arabidopsis Pss30 genes further reduced the cyst number of SCN (Female Index in %) in two independent stack-lines (STL), STL1 and STL2. LS94 is an SCN resistant soybean cultivar. W82, Williams 82, is the soybean GmDR1 and Arabidopsis Pss30 genesrecipient line.

“Our current focus has been to stack all four plant genes into the Williams 82 cultivar. The genotypes will be grown in the greenhouse this winter to identify lines that will carry all four genes in homozygous condition. This means the genotype will carry two copies of each gene and will not segregate for these genes among the progenies,” he explains. “Our expectation is that we will be able to gather sufficient seeds for testing levels of SCN resistance during the summer of 2021. Some of the lines fixed for two or three genes will be evaluated for SDS resistance.”

By the end of the three-year project in September 2021, Bhattacharyya says they should be able to determine if stacking all four genes enhances SCN resistance. They can then deliver genotypes with superior resistance as donors for backcrossing the four genes simultaneously into commercial SDS and SCN resistant cultivars that carry desirable natural resistance genes.

“Williams 82 is not as good as current commercial cultivars, so we have to transfer the four genes to commercial cultivars if they show at least an acceptable level of SCN resistance,” he says. “We believe SCN resistance given by these four novel genes will complement the SCN resistance conferred by genes currently used among the SCN resistant cultivars.”  

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