Project aims to maintain disease resistance in Illinois soybeans

Project aims to maintain disease resistance in Illinois soybeans

By Extension Communications Specialist

URBANA—One of the most troublesome plant diseases in many Illinois fields is Phytophthora rot, which can infect and kill soybean plants anytime from planting to harvest. This disease has been largely controlled by planting soybean varieties with Rps resistance genes.

But recently, the Rps genes have been losing some of their efficiency in several states across the Midwest, creating the potential for renewed outbreaks of the disease in soybean fields.

To counter this problem, researchers from University of Illinois Extension recently launched a project aimed at determining if the strains of Phytophthora in Illinois are developing the ability to kill soybean plants with the available Rps resistance genes. Funding for this project has been provided by the Illinois Soybean Checkoff Board.

“With help from seed company representatives and regional Extension educators, we have collected and tested more than 200 soil samples from soybean fields with a history of Phytophthora or similar seedling health problems,” said Dean Malvick, plant pathologist with U of I Extension.

“Those samples came from more than 20 counties across the state.” The researchers have obtained isolates of the disease-causing pathogen from many of those samples and have tested them against commercial soybean varieties with the three types of Rps resistance genes.

“As expected, we found that many of the isolates from Illinois can defeat the first of those resistance genes and that a smaller number can defeat the second type,” Malvick said. “Unfortunately, we have found in our preliminary work that a few aggressive isolates can defeat all three of the resistance genes commonly found in commercial soybean varieties sold in the state. Although these aggressive isolates exist in Illinois, we still do not know for sure how much damage they may be causing.”

He notes, however, that the aggressive isolates do not appear to be widespread in the state and that two of the three resistance genes are still effective in most cases. “We plan to continue our research to identify the various races of Phytophthora in Illinois,” Malvick said. “Those results will help with selection of soybean varieties with appropriate types of resistance and will be of real value for breeders developing soybean varieties with Phytophthora resistance best suited for the state.”

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