Source: Kansas State University



Russian wheat aphids are insects that are as small as one-sixteenth of an inch, but are capable of much larger damage. The tiny insects have been feeding on wheat plants in the United States since 1986, and their plant destruction has been costing Kansas wheat producers.



Michael Smith and other researchers at Kansas State University have been studying wheat plants that are resistant to the aphids as a way to find a low-risk method of pest management and increased crop yields.



Smith, a K-State professor of entomology, is focusing on identifying a gene that controls a single property in the wheat plant that could deter aphid feeding. The researchers think that when an aphid threatens a resistant wheat plant, the plant responds by expressing genes that make some kind of defensive compound.



"Our goal is to find a gene or genes that are responsible for the resistance - something like a product of a signal that tells the plant to make a toxin or to make a bitter taste," Smith said.



He said there is a two-fold benefit to this low-risk method of pest management. The wheat yield would increase because the pest damage would be reduced, and plant resistance would reduce or eliminate the need for insecticide, which affects the producer's cost and might affect the environment.



"Anytime you use a pesticide, you do run some risk of runoff, which can affect wildlife and drinking water," Smith said. "We have very, very few problems with runoff in Kansas, but that's the whole idea of getting away from the use of insecticides."



When aphids feed on susceptible wheat plants, the insects destroy the plants' capability to make nutrients to produce grains. This is visible on the plant when its leaves yellow and roll into narrow tubes.



Smith's research involves using gene expression experiments. The ongoing project started two-and-half years ago, but Smith said the experimental research only took about a week or two. The quick process involved extracting RNA from infested and non-infested wheat plant tissues, making DNA from the RNA, and placing it on a microarray chip.



By damaging the wheat plant, genes are expressed that are not normally active. K-State researchers looked for a difference of genes in the resistant and susceptible wheat plants.



"We did the experiment with plants that had been fed on for 24 hours," Smith said. "We have since found that some of the genes are turned on as soon as one hour within feeding. For a long time, entomologists and other biological scientists haven't been able to see this kind of rapid response."



The postexperimental part is more extensive.



"It's the process of taking all the data you get and making sense of it, because a microarray chip has 55,000 different little bits of wheat DNA on it, so you can get a lot of information," Smith said. "You have to go out there and search yourself. Most of the two-and-a-half years have been searching the information databases and trying to make sense of this story."



The researchers narrowed the results down to four genes that are unique to the aphid-resistant plant. The final step of the project involves using virus-induced gene silencing that could identify which of these possible genes control resistance.



"Once we know what that gene for resistance is, we can selectively add the resistance gene into a normally high yielding but aphid-susceptible plant, and that's our ultimate goal," Smith said.



Smith presented the ongoing project in 2004 in Australia at the International Congress of Entomology and also at the 2007 national meeting of the Entomological Society of America.



Smith said the four possible genes were identified in the last six months, and he hopes to have the gene-silencing results in the next two to three months.



"Wheat is the largest major plant genome known," he said. "It's very repetitive, and you have to sort through lots of stuff. But we're willing to do that because it's the major crop in Kansas, and we work for the people of Kansas, and in our case, we also work for the wheat and barley producers."



Some of the funding for the research project was provided by grants from the Kansas Crop Improvement Association, the U.S. Agency for International Development, and the Kansas Agricultural Experiment Station.



Others involved in the project from K-State include Xuming Liu, research assistant professor of entomology; Ming-Shun Chen, adjunct associate professor of entomology; Sharon Starkey, laboratory technician in entomology; and JianFa Bai, assistant professor in the K-State Veterinary Diagnostic Lab. Also involved in the research are Xiang Liu, research associate of biology at North Carolina State University, and L. J. Wang, assistant professor of genomics and bioinformatics at Clemson University.