Clearly, Prairie farmers have been looking for a solution to control orange wheat blossom midge.
Even though midge-tolerant blends have only been commercially available since the spring of 2010, the Canadian Wheat Board’s 2011 Variety Survey found that two of the new varieties are already very popular. Seven per cent of the spring wheat seeded by Prairie farmers last spring was Unity VB, and another three per cent of the spring wheat seeded was Goodeve VB.
Farmers have directly contributed to the development of these new cultivars through the wheat check-off managed by the Western Grains Research Foundation (WGRF), and these new blends have shown themselves to be popular. Now, there is documented research to prove their worth.
Cecil Vera, researcher at the Agriculture and Agri-Food Canada (AAFC) Melfort Research Farm, was one in a group of AAFC researchers involved in the study titled “Relative performance of four midge-resistant wheat varietal blends in Western Canada.” The researchers planted four varietal blends of midge-resistant wheat and four varieties of traditional wheat at eight Prairie locations during four consecutive growing seasons, 2007 to 2010. The study was managed by a number of people; Vera was in charge of preparing and distributing the seed and gathering data.
“These varietal blends are doing quite well compared to others. For example, Unity VB, in the northern part of Saskatchewan, yields are 20 per cent higher than AC Barrie. Shaw VB is also listed as 120 per cent of AC Barrie. The other varietal blend of interest to farmers has been Goodeve VB. That one is listed as 11 per cent higher-yielding than AC Barrie.”
In general, the AAFC study found that the midge-resistant wheat blends, as a group, produced higher yields than the typical varieties.
In areas and years where there was little or no trouble with midge, the varietal blends still yielded higher than regular varieties (four per cent higher). In areas the researchers classified as having “moderate” midge damage, the midge-resistant blends showed a five per cent yield advantage.
But it was in the areas and years where there was a high occurrence of losses caused by wheat midge that the new blends really showed their stuff. The researchers found a 14.8 per cent yield advantage. (After comparing this with the yield advantage in areas of low risk, the researchers attribute about 11 per cent of the yield gain to the presence of the new Sm1 gene, and four per cent of the yield advantage to other gains made through plant breeding).
While this is great, of course it’s not perfect. Vera says, “These varieties that are called midge resistant are not completely immune to the midge. There is some damage, but much less.” Vera and other researchers involved in this study are still evaluating the seed and data gathered over the time period — more results in areas of seed quality and the varietal blend will be published in the future.
The table shows average yield results for areas with high and low midge pressure during the four-year study period. The varieties including “VB” are the new, midge tolerant varieties, sold as “Varietal Blends.”
Each year, each of the eight areas was classified according to the local wheat midge experience as shown in the table.
The Sm1 Gene
Midge resistance was first noticed in soft red winter wheat from south eastern USA. The gene, Sm1, that was causing wheat to resist midge was moved into spring wheat using traditional plant breeding techniques.
When wheat midge larvae feed on wheat containing the Sm1 gene, the gene causes the level of the naturally occurring phenolic acids in the wheat kernels to elevate more rapidly than in midge susceptible wheat. The elevated acids cause the larvae to stop eating and starve to death. By the time the wheat reaches maturity, these acids have gone back down to normal levels, so harvested grain is not affected.
This type of biological solution to pest control, based on a single gene resistance, typically does not last long. Generally, some pests resist the new gene, those pests multiply, and the new solution no longer works. In the case of wheat midge, some midge may develop a mutation that would allow them to attack the wheat with the Sm1 gene — these midge would be known as “virulent.” The proliferation of these virulent midge would soon render the Sm1 gene useless.
To prevent this, and hopefully extend the useful life of the Sm1 gene for up to 90 years, plant scientists developed the idea of the interspersed refuge system. With this strategy in place, virulent midge will most likely mate with the avirulent midge found on the refuge (susceptible) plants. The hybrid offspring of these matings would most likely be killed when they feed on Sm1 plants, slowing the evolution of virulence.
The Refuge System
All of the new midge-tolerant varieties are sold as “varietal blends.” That is, 90 per cent of the purchased seed contains the Sm1 gene, and the other 10 per cent doesn’t. That 10 per cent provides a refuge where a normal (avirulent) midge population can survive.
When you buy a varietal blend, it should be easy to find out what other variety has been blended in with the midge-tolerant variety. Farmers buying midge tolerant wheat are asked to sign a stewardship agreement, limiting the use of farm-saved seed to one generation past Certified Seed. (A full copy of this agreement can be found online at www.midgetolerantwheat.ca.) Researchers are investigating the feasibility of extending this time period.
Midge Tolerant Durum?
Midge are also a problem in durum wheat. Dr. Danny Singh, AAFC durum breeder at Swift Current says research is underway in this area with funding from AAFC, WGRF, Agriculture Development Fund (ADF) and the Alberta Crop Industry Development Fund (ACIDF).
When it comes to inserting the Sm1 gene into durum varieties, Singh says, “There are lines that are currently being tested in the Western Canadian Varietal aRegistration System that have the Sm1 gene.”
One of those lines will be in co-operative testing this summer. The new variety needs to pass the registration requirements in the next couple of years. If successful, it will be available to Western Canadian farmers after the necessary seed production steps. †