The wheat DNA that Virginia Tech Researcher Marla Hall passed around at a recent field day looked like a big grain of salt. The disease resistance qualities in the DNA may mean big profits for Virginia wheat growers.
Hall, a post — doctoral scholar working with Virginia Tech Small Grain Breeder Carl Griffey, heads Virginia Tech’s Wheat CAP program. CAP is an acronym for Coordinated Agricultural Program.
Under the CAP program, Hall and other researchers at Virginia Tech, are using MAP, or marker assistant programs, to select genes that have resistance to specific diseases. It is a modern day, high tech method of throwing out potential varieties that don’t have the necessary disease resistance to make profitable varieties for growers.
There are four different genotype centers that evaluate wheat genes as part of the CAP program. The Raleigh, N.C., center serves Virginia Tech and other Southeastern universities. Labs at Kansas State University, the University of Minnesota and Washington State University serve the same function for researchers in other parts of the country.
Hall and her research team grow wheat samples from breeding lines. Leaves are cut from young seedlings in the greenhouse. DNA is extracted from the leaves and sent to the CAP center in Raleigh (North Carolina State University). There, scientists analyze DNA with markers, or short pieces of DNA that are linked to a gene of interest.
Each public breeding program can focus on traits they feel most important to a region. Powdery mildew and fusarium head blight resistance are two traits being sought by Virginia Tech breeders.
From data sent to Raleigh, Virginia Tech researchers can identify breeding lines that are susceptible to these diseases and take them out of the breeding program. “Like throwing out garbage that you know you don’t need,” Hall says.
“This allows us to screen a large number of samples quickly and easily and get rid of the varieties that carry the traits we know we don’t want in a new wheat variety,” she adds.
The next generation can be grown in the field and we know these plants don’t have susceptibility to these common diseases. This gives us a big head-start in evaluating varieties for traits that we do want in wheat varieties, she explains.
An example of putting the sophisticated technology to work in the field comes from Massey, a tall wheat variety that is susceptible to lodging and other production problems, but has excellent powdery mildew resistance qualities.
Massey has a very high QTL, or quantitative trait low-stack, which is the segment DNA in the plant that gives it disease resistance. High QTL makes the job of isolating and marking the genes easier, making Massey highly desirable as a source of powdery mildew resistance.
Massey also has high adult plant resistance to powdery mildew, meaning it is resistance to the disease at the adult state. However, it works to prevent the early spread of the disease. The result is that growers may see some powdery mildew on the lower leaves of young plants, but the disease doesn’t spread at a level high enough to affect the plant’s production capabilities.
Adult plant resistance is a highly desirable trait because it is more durable and works to reduce the pathogen spread and reproductive capabilities. It is not a single resistance gene, but works more to suppress the disease throughout the life of the wheat plant.
Over a period of time, single gene resistance tends to break down. New races of a disease come in and create too much pressure on the resistance gene, causing it to lose resistance and open up the plant to disease damage.
Virginia tech researchers removed a piece of DNA from Massey and transferred it to an experimental wheat variety, VA3555. In the field, it is clear to see that the gene transfer worked — there was no visible powdery mildew on the VA3555 plants. An adjacent plot of Becker variety wheat, which is susceptible to powdery mildew, was visibly affected by the disease.
Last year VA3555 had a statewide yield average of 86 bushels per acre. It also has gene SR36, which gives VA3555 stem rust resistance. In post-harvest tests VA3555 also had better baking qualities than its parent plant — Massey.
By comparison, Massey, in the same variety trials statewide in Virginia, averaged 70 bushels per acre. Massey frequently also has leaf rust problems that can reduce yields under some growing conditions.
USG3209 is another progeny of Massey that is being tested by Virginia Tech researchers. It has poor baking and milling quality, but is a high yielding variety, consistently topping 80 bushels per acre in statewide variety trials. It also has good test weights in the high 50s and is a lot shorter than Massey, thus avoiding many of its parent’s lodging problems.
The first of the Massey progeny developed using genetic markers likely to be available to growers is VA03W409. It yielded 89 bushels per acre last season. The new variety has excellent milling and baking qualities and also has performed well in tests in Missouri (97.5 bushels per acre) and Wisconsin in 2008.
Massey, Coker 9835 and Sisson, all popular wheat varieties in the upper Southeast, are genetically linked to VA03W409. In addition to high yields, the new variety consistently has test weights in the high 50s and is resistant to leaf rust and stem rust.
Virginia Tech researchers used the same marker technology to transfer scab resistance to fusarium head blight in Renwood, a popular upper Southeast wheat variety, to its progeny VA05W641.
In side-by-side yield comparisons, Renwood produced 86 bushels per acre, compared to 93 bushels per acre for VA05W641.
Renwood is a very strong gluten wheat — almost like a hard wheat. These characteristics give Renwood, and its progeny, poor baking quality.
The Wheat CAP program grant was approved in 2006 and will last at least until 2010, with funding in excess of $5 million. The goal of the program is to advance technology to rapidly identify genes that may produce higher quality, disease-resistant wheat.
Twenty percent of all calories consumed globally come from wheat-derived foods, such as bread and pasta. The Wheat CAP research program offers a potential solution to nutritional deficiencies affecting hundreds of millions of people around the world.
For Virginia wheat growers the program offers the potential of raising wheat production and quality levels without adding expensive inputs, helping lower the risk of grain farming in the upper Southeast.
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