The Invisible Pest

Revisiting the Fight Against Soybean Cyst Nematode

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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Iowa State University plant pathologist Greg Tylka highlighted the challenges facing researchers in the fight to defeat soybean cyst nematode, at an SCN Conference in Miami. (DTN photo by Emily Unglesbee)

MIAMI (DTN) -- For such a tiny pest, the soybean cyst nematode (SCN) generates some impressive numbers.

The pathogen is ranked as the number-one soybean disease in the U.S. and number two, worldwide. It infests at least 29 states in the U.S. and researchers routinely peg annual yield losses around $1.5 billion. Yet, a recent University of Missouri survey showed that only 34% of responding farmers had sampled to see if they had SCN.

Therein lies the challenge for industry and plant pathologists -- and the driving reason behind an industry-wide meeting focused on the soybean cyst nematode taking place this week in Miami, Florida. There, more than 100 scientists, growers and representatives from companies and commodity groups spent a warm, sunny Wednesday huddled in a chilly conference room, sorting through the problems posed by SCN. The conference is the first of its type since 2008, and is part of a push by scientists to re-energize farmer and company interest in this silent yield-robber.

Iowa State University plant pathologist and nematologist Greg Tylka kicked off the meeting by highlighting three primary areas of difficulty for researchers: low farmer awareness, the complex biology behind SCN and the alarming state of SCN-resistant soybean varieties in the U.S.

He identified the latter point as the industry's Achilles' heel. Of the 970 soybean varieties identified in Iowa as SCN-resistant in 2016, more than 97% of them used a genetic source of resistance known as PI88788.

"Imagine if 97% of herbicides available were glyphosate," Tylka told conference attendees. "But this situation is even more dire because we have almost no susceptible soybean varieties being sold. If all these varieties truly are all resistant, there is constant selection pressure across the country, and that selection pressure is happening the minute you plant the seed."

The results of this problem are already clear, Tylka noted. SCN populations in farmers' fields across the country with more than 10% reproduction on PI88788 are common and have been rising steadily since the early 2000s. A recent Iowa State analysis of the corresponding yields in these fields confirmed his worst fears, Tylka concluded.

"The yield of SCN-resistant soybeans will decrease as nematode reproduction increases," he said.

Varieties with new SCN-resistant traits face a number of hurdles, with economic concerns topping the list. Farmers do not currently pay more for SCN-resistant genes in their soybean varieties and are unlikely to do so in the future, Tylka noted. That would make it hard for companies to recoup the cost of breeding novel resistance genes into elite soybean varieties.

Nonetheless, a large number of sessions on the conference's first day focused on the hunt for new sources of resistance beyond PI88788 and Peking (a second, but less widely used source of genetic resistance). DuPont Pioneer has announced they are including more Peking resistance to their soybean varieties in the future.

Other research efforts have focused on stacking available SCN-resistant genes -- known as Rhg1, Rhg2, etc. -- together within varieties. Work from the University of Illinois found that this strategy improved broad-spectrum resistance of the resulting soybean plants, and the genes did not affect yield.

Iowa State University plant pathologist Madan Bhattacharyya presented a promising transgenic soybean trait that he found when working to produce SDS-resistant varieties. By inducing the expression of a key protein, Bhattacharyya found the resulting GE soybean plants showed resistance to SDS, spider mites and soybean aphids, as well as significantly reduced SCN reproduction.

Additional sessions delved into the complex biology of the soybean cyst nematodes themselves, including the numerous types (or races), their genetic diversity and differences in virulence (ability to reproduce on a SCN-resistant plant).

Thursday's sessions will focus on the farmer's perspective on SCN and management options, including new and old nematicide seed treatments and cover crop research.

See more information on the SCN Conference and agenda here:….

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Emily Unglesbee