What is in this article?:
- While several varieties of wheat have resistance to the virus bred into them, there has been a problem with that genetic resistance breaking down in temperatures above 75 degrees.
- Wheat streak mosaic virus is the most prevalent disease in the southwestern wheat producing region of the U.S.
- Further research might determine that wheat varieties with wheat streak mosaic resistance may be more effective in northern states where wheat is planted later when it is cooler.
THE LEAVES of the Ron L variety of wheat with bred-in resistance to wheat streak mosaic virus show significantly more damage than the leaves of TAM 112 after both were exposed to the same amount of mites and grown under the same environmental conditions, according to Dr. Charlie Rush, Texas AgriLife Research plant pathologist. (Texas AgriLife Research photo by Kay Ledbetter)
Understanding how the temperatures affect this process is important, Rush said.
“If you have a lower number of mites, and a lower number of those are carrying the wheat streak virus, it will reduce the incidence of disease and reduce the potential for development of an epidemic,” he said.
Price said so far it looks like when the wheat plants, regardless of variety, become infected early with high mite and virus populations, it is difficult or even impossible for the plants to recover before they go into winter dormancy.
However, Rush said they have seen interesting results in the first replication of side-by-side comparisons of Mace, Ron L, TAM 112, TAM 111 and Karl 92.
“We think that TAM 112 is exhibiting some tolerance to the vector,” he said. “If this holds up – these are preliminary results and must be repeated – the thing that is so exciting about this is if you have the resistance to the mite, then you don’t have to worry about the virus building up.”
In his greenhouse study, Rush said the plants are exposed to 20 mites per pot at the same time and grown under the same environmental conditions. As they have grown out, TAM 112 exhibits healthy leaves while pots beside it planted to other varieties have twisted leaves and the typical streaking and striping associated with wheat streak mosaic virus.
Mace has a specific gene for resistance to wheat streak, wsm1, and Ron L has a different gene, wsm2. The Karl 92 is planted as a check variety as it has no known resistance, and TAM 111 and TAM 112 were added to the study to see how they performed because they are regionally adapted, he said.
Angela Simmons, a new graduate student in Rush’s program, is in the process of washing the mites from three tillers per pot and then counting them under a dissecting scope. The number of mites for Mace and Ron L are in the range of 2,000 to 3,000 and the number of mites for TAM 112 is in the range of 100 to 200, “so there is a tremendous difference in the mite population showing up, he said.
The leaves of TAM 112 have essentially no curling resulting from the mites and look almost normal, he said, but there are some symptoms of wheat streak exhibited indicating it has been infected by the virus.
“If you think about an entire field of this, with a field next door of a susceptible lines where you have massive numbers of mites, it can make a very real difference,” Rush said. “If they blow into your TAM 112 field and the mites aren’t building up to as high a population, the virus isn’t building up, so as they move across the field, the number of mites gets less and less.
“Overall, you may have some infection, but you will end up having a much healthier wheat field resulting in better yield and quality than if you had a cultivar with a specific resistance gene to wheat streak but it was planted in late August or early September when the temperatures are too high for the resistance to be effective,” he said.
That’s what this whole study is about, Rush said, trying to look at how the temperature fluctuations that the crop goes through in the Panhandle at this time of the year are going to affect overall disease development.