How Are You Conserving Genetic Resistance? A Cautionary Tale

Existing wheat midge resistance depends on a non-GM, single gene. Single gene resistance is more easily overcome than multiple gene resistance traits
Existing wheat midge resistance depends on a non-GM, single gene. Single gene resistance is more easily overcome than multiple gene resistance traits

By Karen Lewis

As farmers across the central U.S. corn belt scramble to prevent the spread of western corn rootworm resistance to Bt corn, Prairie wheat growers are being urged to be diligent in their stewardship efforts to protect midge tolerant wheat technology.

“Resistance to corn rootworm technology is really a cautionary tale for Prairie farmers who grow midge tolerant wheat,” says Todd Hyra, business manager for SeCan and a member of the Midge Tolerant Wheat Stewardship Team.

Performance issues with Cry3Bb1 – the first Bt protein to provide corn rootworm control – were first reported in 2009 and today growers from Nebraska to Illinois appear to be losing the battle to prevent the spread of resistance. According to Michigan State University field crops entomologist Christina DiFonzo, two specific management practices – growing continuous corn and using the same Bt trait (Cry3Bb1) – have been the key contributors to growing resistance.

DiFonzo recommends two key stewardship practices for growers to keep further resistance growth in check: simple crop rotation as well as rotating traits used to control rootworm rather than relying on the same trait year-after-year. Bt corn growers are also required to plant non-Bt corn refuges to help manage resistance to the technology. In order to combat further resistance, however, growers have to be more diligent and better manage refuge requirements.

Here in Canada, Prairie wheat producers have been growing midge tolerant wheat since 2009. Producers helped to fund the development of midge tolerant varieties through their support of the wheat check-off. In all, it took more than 15 years and a huge financial investment for researchers to move a single gene for midge tolerance, Sm1, into spring wheat varieties to protect plants against the pest.

Wheat midge infestations can reduce crop yield and lower market grade of harvest grain. For an average grower, losses can range from $20 to $75 per acre. Between 2004 and 2010, Prairie growers lost approximately $70 million annually due to midge damage.

The challenge is to ensure that growers who have been using the technology respect the Stewardship Agreement that they have signed,” says Hyra. “We don’t want to find ourselves in the same situation that U.S. growers are now in with corn rootworm resistance.”

Sm1 is a single gene that could be overcome if growers don’t respect the refuge requirements,” explains Hyra. He notes that following the requirements are relatively easy for growers because the refuge is interspersed in the Certified seed that they buy and allows for the natural midge population to remain in balance, which counteracts resistance.

But farmers can put the technology at risk when they rely too heavily on farm-saved seed. The Stewardship Agreement specifies that farm-saved midge tolerant seed can be used just one generation past Certified. “If you’re planting second generation saved seed, you put the whole refuge plan at risk and increase the chance of creating a virulent midge population that could overwhelm the Sm1 trait,” says Hyra.

So far, producers have been doing their part by sticking to the stewardship plan. A grower survey conducted by the Midge Tolerant Wheat Stewardship Team, a broad industry coalition representing plant breeders, government, seed growers, seed distributors and producer groups, indicates the percentage of producers who believe stewardship is critical to safeguarding the technology has increased every year since 2010, the first year the survey was conducted. In 2013, more than 93 percent of producers surveyed agreed that it’s critical to have a stewardship program in place to ensure the effective life of the midge tolerant gene is protected.

We’re very pleased with growers’ stewardship commitment, but we need them to remain vigilant,” says Hyra. He adds that corn rootworm resistance to Bt corn will spur corn companies to invest heavily to develop alternative traits and technologies to manage the problem, but that is unlikely to happen should Sm1 resistance develop.

 “There really is no Plan B,” warns Hyra. “The midge tolerant varieties we have now are dependent on the Sm1 gene and so will future varieties. That’s why it’s so important to protect the technology for the future.”

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