Sudden death syndrome (Fusarium virguliforme)

Sudden death syndrome: biology

Sudden Death Syndrome (SDS) is a root rot disease caused by the fungus Fusarium virguliforme, which overwinters as spores in crop residue and soil.

SDS is one of the most significant soybean diseases in North America with an average yield loss of about 20 percent and can reach up to 60 percent.

The disease is most often found in fields infested with soybean cyst nematode (SCN), which produces wounds that allow the fungus responsible for SDS easy access to the internal root tissue. SDS can also occur without SCN being present.

Weather is a crucial factor in the impact of SDS on soybean yields. Cool, wet conditions at planting are ideal for infection. The pathogen also favours wet conditions throughout the growing season.

Although infection often occurs during the first six weeks after emergence, symptoms generally do not become noticeable until the mid-pod reproductive stage of soybean development.

SDS-infected plants will begin to show distinct yellow speckling or spotting between the veins (interveinal chlorosis). As the disease progresses these areas become larger and in severe cases the entire area between the veins becomes brown (necrotic) and dry. The leaves curl from the outer margin. These brown areas eventually fall out leaving only the veins, which remain green, on the leaf. The next symptom is often premature defoliation and death of the plant. In most cases, the petioles (leaf stalks) on these dead plants remain attached to the stem.

To confirm SDS, cut open the root and stems and look for rotting roots and brown discoloured streaks in the stem; the centre pith will remain white.