Sudden Death Syndrome

Soybean plants infected with the SDS pathogen, showing leaf symptoms and beginning signs of pod abortion. Photo credit: Craig Herzog, Southern Illinois University.

udden death syndrome (SDS) is a soybean disease characterized by leaf spots and root decay. The name sudden death syndrome is descriptive in that normal-appearing plants turn yellow and die rather quickly. The disease is of major concern because of its potential ability to reduce yields significantly. Yield losses due to SDS range from slight to 100%, depending on the soybean variety.

Critical infection stage is soon after planting

New research suggests that the critical stage for the SDS pathogen to infect soybean plants is before emergence of the germinated seed. Infections occurring at early growth stages are more likely to produce foliar symptoms late in the summer. Soybeans planted early in cool soil have slow germination and emergence, which prolongs the contact period between pathogen and soybean, promoting infection.

In 2007, sudden death syndrome was wide spread in the North Central region. Many of those infested fields will return to soybean after being rotated with corn last year. Early planting in these fields will likely have a higher risk of SDS.

How SDS spreads

SDS is a soil-borne disease and is spread mainly when soil is spread: equipment, human and animal feet, birds, and wind and water erosion. Cysts of soybean cyst nematode have been found to carry the SDS fungus.

Root rot occurs on plants infected with the SDS pathogen. A blue discoloration is visible on this infected root. Click on image to view a larger version. Photo credit: X.B. Yang, Iowa State University

The pathogen

Sudden death syndrome is caused by the soil fungus, Fusarium verguliforme. The fungus produces a toxin that is translocated throughout the plant and interferes with the vascular system of the plant. This can cause sudden yellowing and death of the leaves as the water supply is cut off. The pathogen also causes a root rot.

Fusarium virguliforme has a blue pigmentation and a blue coloration is sometimes found on the tap roots of plants that are severely infected with the pathogen, due to the large number of conidia (spores) produced on the surface.

The fungus also produces a thick-walled survival structure, called chlamydospores, in the cortical tissue of soybean roots. The chlamydospore can overwinter and can survive for several years in the soil.

The SDS pathogen is very closely related to another soybean pathogen that causes seedling disease and root rot of soybean, Fusarium solani form B.