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Iowa State researchers study soybean genes to help SDS

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Any number of different soybean pests can derail a good season. Soybean farmers know how devastating they can be, with some causing millions in losses each year.

A new study by a research team led by Madan Bhattacharyya, Iowa State University professor in the Department of Agronomy offers new hope for future protection against some of soybeans’ worst threats, including soybean sudden death syndrome (SDS) and soybean cyst nematode. Enhancing resistance to SDS, one of the leading causes of yield loss for soybeans, was Bhattacharyya’s initial goal in manipulating soybean genetics.

SDS is caused by a soil fungus (Fusarium virguliforme) that attacks a soybean plant’s roots. The symptoms of SDS are typically seen on leaves after flowering when leaves show scattered yellow spots between veins. Diseased plants will have rotted taproots and lateral roots, so by the time a farmer sees discolored leaves, it is already too late.

“Sudden death syndrome regularly finishes as one of the most destructive soybean diseases across the north central region, with an average of a $72.8 million loss each year just in Iowa,” said Daren Mueller, coordinator of the Integrated Pest Management program at Iowa State and co-director of the Crop Protection Network.

This is why Bhattacharyya’s work might be a game changer for soybean farmers. He and his team were able to identify a gene, that if “turned on,” could provide improved resistance against SDS and other soybean pests.

“This gene has only been found in legumes, and a limited number of other crops like cocoa, jute and cotton,” Bhattacharyya said. “The expression of this gene is very rapidly suppressed following F. virguliforme infectionTo overexpress the gene, we swapped a part of the gene with that of three other soybean genes that are induced during infection.”

The researchers field-tested their transgenic lines with the gene overexpressed during four growing seasons. They found that up to 91% of the transgenic plants showed SDS resistance — without affecting yield potential. Moreover, they were surprised to see that the transgenic soybean plants exhibited resistance not only against F. virguliforme, but also against spider mites, soybean aphids and most importantly, soybean cyst nematode.

Soybean cyst nematode, the number one soybean pathogen in the U.S. causes yield suppression valued at over $1.2 billion annually.

Their findings were published recently in the peer-reviewed “Plant Biotechnology Journal.” Bhattacharyya’s co-authors were research scientists Micheline N. Ngaki, Dipak K. Sahoo, and Bing Wang of the Bhattacharyya Lab, in the Department of Agronomy.

Bhattacharyya’s team is continuing to study the mechanisms used by the overexpressed gene in inducing broad-spectrum resistance in transgenic soybean lines. They have observed that apparently over 20 signaling genes for defense responses are regulated by this gene. They believe further research and testing might establish the gene as a “master switch” for defense pathways against multiple pathogens and pests.

This research received support from the U.S. Department of Agriculture National Institute of Food and Agriculture and the Iowa Soybean Association (ISA).

“The ISA Board has supported the work by Dr Bhattacharyya for several years. Going into this project, our farmers realized that this was longer-term, higher-risk, more basic research that could fail.  But they initiated and maintained the investment because they saw the innovative and unique potential of the research to potentially provide novel genetic tools to combat SDS,” said Ed Anderson, ISA’s senior director of research. 

“As the work progressed, it became apparent that this gene may be unique in potentially achieving biotech-derived single gene broad resistance against multiple pathogens and pests,” Anderson said “If the results of Dr Bhattacharyya’s work continue to be validated, this will the first report of a single biotech gene to engender soybeans with resistance to SCN, SDS, aphids and spider mites.  This would be both ground-breaking from a science perspective and potentially highly valued from a commercial perspective.  An impressive example of the power of soybean-checkoff dollars in university research discovery and development.”

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