Researchers work to unravel the mysteries of taproot decline

taproot decline
Root symptoms associated with taproot decline on young soybean seedlings. Note the dry-rotted taproot that broke when seedling was removed from the soil profile — photo by Tom Allen, Mississippi State University

Superb sleuthing among plant pathologists in three states helped track down the culprit whose symptoms include soybean seedling death, yellow leaves and lower yields.

Taproot decline, a disease first noticed in Arkansas, Louisiana and Mississippi in 2007 and formally identified in 2017, was one of the topics on the agenda during the recent 2018 Rohwer Field Day hosted by the University of Arkansas. More than 100 growers, consultants, Extension personnel and researchers weathered the southeast Arkansas heat and humidity for the event.

Terry Spurlock, associate professor and Extension plant pathologist for the Division of Agriculture, discussed Rohwer variety trials that screened for taproot decline tolerance or resistance.

University of Arkansas scientists banded together with colleagues at Louisiana State University and Mississippi State University to uncover the mystery that was damaging soybeans.

“We did all the work between the three institutions. The disease is caused by a fungus that had never been described before,” Spurlock says. “It wasn’t in any of the DNA databases.”

Eventually, the pathologists found that the as yet-unnamed fungus was a Xylaria, known as wood-rotting fungus that produces “dead man’s fingers” commonly seen in forests. When the fungus infects a soybean seeding, it causes the taproot to rot and kills its young host plant.

“Infections of more mature soybean cause symptoms such as stunting, severe chlorosis and yield loss,” he says.

Initially, leaves of plants infected with soybean taproot decline may have an almost pumpkin orange cast — photo by Tom Allen, Mississippi State University

Taproot decline is increasing in importance in Arkansas At the field day, Spurlock says, “I was telling farmers about how bad it’s gotten. It’s been as bad this year as it’s ever been.”

The disease has been found predominantly in southeastern Arkansas and as far north as Missouri and Tennessee. It also was found in Alabama last year.

With the variety trials, researchers were looking to not only determine what varieties were susceptible but also to see if any had tolerance or resistance so they could be recommended to growers.

During the field day,  growers got to view good plots as well as ones ravaged by the disease.

The trials were done in triplicate, with plots also planted in Louisiana and Mississippi. At the end of the year, researchers from the three states will share their data and present it at winter production meetings.

The research on taproot decline is being supported by soybean promotion boards in all three states.

The University of Arkansas contributed this article.

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