Sudden death syndrome (SDS), which is caused by the fungus Furarium solani, has emerged in recent years as a major disease problem for soybean growers in Illinois. Despite the increased availability of new resistant soybean varieties, the information for growers to make decisions on which seed to plant has been limited by the available methods of testing for this disease.

To meet the need for better diagnosis of SDS, researchers at the University of Illinois have recently developed a new technique for detecting the disease that is faster and more accurate than the methods currently in use.

"With present methods, you need to grow a sample on a gel plate to get your results," said Terry Niblack, nematologist in the Department of Crop Sciences at the University of Illinois. "The fungus grows so slowly that there is a major lag time before you can obtain any results. With this new method, the diagnosis can be made within one day rather than the two or three weeks for current tests."

Major work in developing the improved test was conducted by Senior Research Specialist Xuebiao Gao. Field studies were carried out by graduate student Tamra Jackson. Additional support was provided by Glen Hartman, USDA plant pathologist at the University of Illinois, and Susan Li, director of the Soybean Disease Germplasm Collection at the University of Illinois. Primary funding for the project came from the Illinois Soybean Checkoff Board.

The new test utilizes a molecular technique know as real-time polymerase chain reaction (PCR). With this technique, the results can be measured as soon as they show up in the test, rather than only after it is finished as in other molecular testing methods

"That allows us to determine not only the presence of the fungus but also the exact quantity in a sample," Niblack said. "Having detailed information on the amount of fungus present is important because we are starting to have more and more soybean varieties with resistance to SDS. The more precisely you can characterize the disease in a field, the better you can control it."

She points out that one major problem for growers is the fact that the fungus can be present in a field without showing obvious symptoms.

"As part of this research, we are working on relating the amount of the fungus in the roots to the amount of disease that shows up," she said. "With this test, we can tell growers how much of the fungus they have in their fields even when there are no signs of disease. You don't necessarily have to see symptoms for a resistant variety to pay off."

She notes that the new test should become affordable for commercial laboratories as the prices for the new technology come down over time.

"As SDS becomes more of a problem around the state, it will become increasingly important to have a fast and accurate test for diagnosing the disease," Niblack said. "It will also have important benefits for researchers, especially in looking at the interaction between SDS and the presence of soybean cyst nematodes."