Mississippi State researchers ID new soybean disease

soybean taproot decline
Soybean taproot decline is a new crop disease that has recently been identified by researchers in Mississippi. (Courtesy Mississippi State University)

Mississippi State University Extension researchers have identified a new soybean disease that has reduced yields in several fields in the state recently.

Named “soybean taproot decline,” it has symptoms similar to some other bean diseases. They include yellowing of leaves while the veins stay green.

Unlike some other diseases that affect the crop during specific growth stages, soybean taproot decline is something producers will need to watch for year-round, according to a news release.

“This disease has eluded all of us, and I think the reason for that is it has been misdiagnosed as a number of similar diseases we have seen before in soybean, such as sudden death syndrome,” Tom Allen, MSU Extension Service plant pathologist and Mississippi Agricultural and Forestry Experiment Station researcher, said in the release. “It’s not on a single fungicide label, and it has never been reported as an issue in soybeans. I’ve been looking at this ever since I got here in 2007.”

Allen and Experiment State researcher Maria Tomaso-Peterson worked together to determine that the disease can be spotted during the vegetative stage of soybean growth.

“If you grab a soybean plant and pull it out of the ground, and you leave the vast majority of the taproot there, or you have a portion of the taproot and you break it, and it snaps and sounds dry, you have taproot decline,” Allen said. “The organism that causes this essentially produces a dry rot and rots the taproot away. The base of the stem will look black, indicating fungal growth.”

Preliminary data suggests the average amount of yield loss due to the fungal disease is about 18 percent of harvestable yield. The trials were conducted in small plots, and producers may net see as heavy a loss in large-scale production.

Researchers will continue to conduct field trials along with greenhouse and laboratory studies with colleagues in Arkansas and Louisiana.

Part of the work will focus on determining the causal organism. Once the fun gus is identified, the next step is to conduct full-scale field trials to determine how to manage the disease and minimize losses.

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