Soybean cyst nematode (SCN) is the leading cause of yield loss for the oilseed crop across North America. And unless a new source of resistance is found to fend off the pest, growers can expect to see SCN gobble up an increasing percentage of their yield in the years ahead.
That was the message delivered by Iowa State University professor Greg Tylka to growers attending the Southwest Agricultural Conference in Ridgetown, Ontario last week.
In this episode of the Soybean School, Tylka explains that in Iowa the yield advantage of growing SCN-resistant varieties is slowly withering away thanks to the pest’s growing resistance to genes from the PI 88788 breeding line resistance source. In Iowa, about 97 percent of the varieties available carry PI 88788 resistance. These varieties typically yield seven bushels per acre higher than susceptible varieties, but nematodes are slowly breaking down that advantage.
In the 1990s, Tylka notes that nematode populations typically had less than 10 percent reproduction on varieties carrying PI 88788, but Iowa fields now see reproduction of 50 percent or greater. In Ontario, things are not as dire. Resistance is trending upward, but reproduction levels for nematodes are reported at about 15 percent on PI 88788 resistance varieties.
Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) plant pathologist Alberta Tenuta says there are a number of reasons for the lower levels of resistance in the province, including crop diversity and longer rotations that include more non-host crops. But resistance is becoming a concern.
Tylka notes that other sources for breeding resistance are available, most notably PI 548402 (Peking), but these sources provide agronomic challenges and are undesirable because of flat, viney growth, black seed coats and late maturity.
The challenge for the industry now is to come up with new resistance sources to take the pressure off PI 88788 or utilize other available sources. But that will take a significant commitment of research and investment, and Tylka questions where that will come from. He notes that current PI 88788 varieties are priced the same as non-resistant or susceptible varieties so that means growers are not paying a premium for SCN protection.
Without a premium, Tylka says it’s difficult for seed and technology companies to justify the investment. “Companies need to pay the bills and it will take millions of dollars to bring high-yielding varieties to market with other sources of resistance. They need to recover that perhaps in the form of premium prices for that seed.”
Tylka suggests that Mother Nature may eventually force seed companies to act if the varieties they currently sell with PI 88788 resistance are overwhelmed by the pest.