“In quantitative resistance where multiple genes are working together to form resistance, breeders have to distinguish the gray area between susceptible and resistant,” Hartman said.

“It takes a lot to do that visually with your eye. You can look at samples under a microscope and take multiple measurements But, it’s hard and time consuming, particularly when you are working with breeding populations and hundreds of samples.”

Hartman said this technique will be useful for plant breeders trying to breed soybeans for resistance to soybean rust.

“We believe Q-PCR will save time and be more precise,” he said. “The precision part is very important. The more precise you can be, knowing exactly what the line is reacting to, will lead to more precise mapping of the quantitative resistance genes.”

The mapping of this particular quantitative resistance is very important to breeders selecting for rust resistance, Hartman said.

 “It’s a numbers game,” he said. “In developing soybean cultivars, a large number of lines need to be evaluated so many inferior lines have to be discarded. In terms of breeding for soybean rust resistance, this technique can help determine which lines are more resistant to rust when it comes to the gray areas or quantitative resistance.”

This research, “Comparisons of Visual Rust Assessments and DNA Levels of Phakopsora pachyrhizi in Soybean Genotypes Varying in Rust Resistance,” was published in the April 2011 issue of Plant Disease. Other researchers include Chandra Paul and Curt Hill of the U of I Department of Crop Sciences. This research was supported by the United Soybean Board and the Soybean Diseases Biotechnology Center at the U of I.