Wheat Midge Tolerance Gene Detected in Soft White Wheat

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Through recent advancements in marker technology, SeCan recently discovered that the majority of the soft white wheat varieties grown in Western Canada contain the Sm1 trait for midge tolerance – and for this reason they will require stewardship. The Midge Tolerant Wheat Stewardship Team provides the background and an explanation of why stewardship is necessary:

Sm1, the only known gene that confers tolerance to wheat midge, was first identified in soft red winter wheat varieties. In the late 1990s, Canadian public breeders worked to cross this naturally occurring trait into red spring wheat (CWRS and Extra Strong) for the benefit of western Canadian producers. These first products were launched in spring 2010 (AC Unity VB, AC Goodeve VB, AC Glencross VB).

Since that time, over 20 varieties of Midge Tolerant Wheat have been registered in many classes, including CWRS, CPSR, CWES, CWAD, and GP/SP.

As Sm1 products neared commercialization, entomologists agreed that the risk of midge becoming resistant to the trait was highly likely. They suggested a stewardship plan incorporating an interspersed refuge (10 per cent of a susceptible variety) was necessary to preserve the useful life of the Sm1 trait.

First evidence of Sm1 in soft white spring (SWS) wheat varieties came from field tests from the General Purpose Co-op during the 2015 growing season – conducted by the Agriculture & Agri-Food Canada (AAFC) Manitoba wheat midge program (Curt McCartney and Sheila Wolfe), and the University of Manitoba midge program (Alejandro Costamagna, Ian Wise, and Roxanne Georgison). These varieties were identified as midge resistant based upon dissection of wheat spikes.

In 2016, in coordination with SWS Breeder Dr. Harpinder Randhawa, the entire SWS Co-op was tested. The data was all based on dissection of spike samples from the Co-op field tests.

Also, in 2016, Dr. Curtis Pozniak from the Crop Development Centre (CDC) at the University of Saskatchewan, tested a marker for Sm1 on

Wheat Co-op entries. This was done to see if his DNA marker accurately predicted the field-based phenotype (i.e. kernel damage).

The DNA marker developed by CDC was done in conjunction with researchers at AAFC. To date, the marker results appear to match the results from the spike dissections.

Based on the work above, the following varieties carry Sm1 and are midge tolerant: AAC Awesome (CWSP), AAC Chiffon, AAC Indus and AC Sadash. AAC Paramount is suspected to carry Sm1 but needs to be confirmed by field test in 2017.

AC Andrew has been tested by marker and in the field, and does not contain Sm1. For this reason it will be an appropriate refuge for all tolerant varieties.

Why Stewardship Now?

If Sm1 varieties have been grown in other regions without a refuge, why do we need a refuge in Western Canada? Other regions, such as the UK and Eastern U.S., do not have a large acreage of wheat in rotation. In Western Canada, the traditional fit for SWS wheat was the irrigation area of southern Alberta – this area typically has little to no midge pressure. However, in the last seven to eight years, we have seen growth in soft white acres into non-traditional areas to supply the feed and ethanol market. In comparison to other classes, the SWS acres are relatively small. This is fortunate, but still needs to be addressed.

The fact we have been growing SWS without a refuge puts the Sm1 trait at risk. Midge tolerant wheat saves producers $40-60 million per year ($36 per acre). There are no replacement tolerance genes. “There is No Plan B.”

For this reason we need to act as quickly as possible to put a stewardship plan in place for the benefit of all wheat producers (not just soft white).

The Stewardship Plan

Seed growers will add refuge to all future seed stocks released of AAC Awesome, AAC Paramount (once field results confirm resistance), AAC Indus, AAC Chiffon and AC Sadash.

Varieties that have not yet been released have limited volumes. Remediation will be a much greater challenge for a variety like AC Sadash that is currently grown on several hundred thousand acres, making up over half of the total SWS acres.

For AC Sadash there were two options to protect Sm1: 1) Work with SeCan members and the industry to add refuge to all seed stocks available, as soon as realistically possible; 2) Deregister AC Sadash to remove it from the system, and replace it with the new products that have refuge blended in.

SeCan has decided it is in the best interests of the industry that AC Sadash remain available – and trust the industry will be willing to participate in implementing a stewardship plan.

The hope is that growers will “do what is right” to protect the trait for the benefit of future generations of wheat producers.

How Can You Prevent Creating Resistance?

If you grow one of these SWS varieties, add a refuge: one bushel of AC Andrew to every nine bushels of tolerant SWS variety.

If you’re unable to add the refuge, spray insecticide to eliminate the possibility of resistant midge (until you are able to add refuge).

In the near future, we hope to have the Sm1 marker commercially available. This will give us the opportunity to monitor farm level samples of AC Sadash for the appropriate level of refuge to ensure the stewardship is being followed.

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