NPIPM:Sudden death syndrome on soybean
Compiled by: Buyung Hadi, from the materials by: Loren Giesler, Dean Malvick and Lawrence Osborne
First reported in the US in 1971, sudden death syndrome (SDS) is now a widespread disease of soybean in all major soybean growing areas of the US. Due to its potential to dramatically reduce yield, SDS is ranked among the top five yield-robbers of soybean.
Causal Organism
Sudden death syndrome is caused by the fungal pathogen Fusarium virguliforme (previously named Fusarium solani f. sp. gycines). Apart from soybean, F. virguligorme also infect other economically important hosts such as snap and lima bean.
Symptoms and Signs
The onset of SDS foliar symptoms of SDS vary with geographic location, but in the Midwestern US they typically appear after flowering. Early symptom consists of yellow spots of leaf areas between veins. While the veins remain green, spots increase in size and grow together, eventually turning brown as these tissues between veins die. Roots of infected plants are smaller than normal and show various degrees of necrosis. The outer vascular tissue (xylem vessels) turn light brown, but the pith remains white. Vascular tissue turning light brown while the pith remains white is a diagnostic symptom differentiating SDS from brown stem rot. When roots are removed from soil, blue fungal masses can be found on the root surface. As the name implies, the progression between early symptoms of SDS and plant death can be rather swift. Plants defoliate early while petioles remain attached to the stem.
Disease Impacts
Sudden death syndrome affects yield by reducing seed size and the number of seeds per pod. Slight to total yield loss may occur depending on the soybean variety and environmental conditions.
Life Cycle and Epidemiology
Fusarium virguliforme can produce thick-walled spores called chlamydospores that can survive for several years in the soil. The pathogen can infect soybean roots anytime during the plant growth, but infection that occurs before emergence of the germinated seed is considered critical. Even if infection occurs early, symptoms do not appear until later in the season.
Within the plant, F. virguliforme produces toxin that is translocated to the leaves through the vascular tissues. This toxin is partly responsible for the appearance of SDS foliar symptoms.
Cool temperatures and high soil moisture in the beginning of the season seem to favor infection. High soil moisture at around R1 stage (beginning bloom) is also important for SDS epidemiology. Once infected, plants exposed to dry soil may show more severe foliar symptoms. Co-infection between F. virguliforme and soybean cyst nematode has been shown to increase the severity of SDS. Nutrient availability that normally lead to high yield also seem to increase the severity of SDS symptoms.
Management Approaches
Scouting
The symptoms of SDS can be confused with brown stem rot. It is important to identify the disease properly in order to make an accurate management decision. Below is a table of diagnostic symptoms and signs to differentiate the two diseases:
| Plant part | SDS | Brown stem rot |
|---|---|---|
| Roots | Smaller than normal, necrotic, blue fungal masses sometimes visible on the surface of the roots | Healthy, no blue fungal masses on the surface of the roots |
| Interior stem | Browning of vascular tissue, pith tissue remains white | Browning of vascular and pith tissues |
Cultural Methods
Cool and wet soil at the time of planting is favorable for early infection. Try to manipulate planting date until the soil is warm and dry. Tilling may help to promote earlier warming of the soil. Soil compaction is shown to favor F. virguliforme infection. Subsoil tillage to the depth of 15.7-17.7 in. (40 to 45 cm) is shown to decrease soil compaction and reduce SDS severity. Crop rotation, especially to corn, has not been shown to reduce SDS.
Host Plant Resistance
Commercial soybean varieties with degrees of resistance against SDS are available. Using these varieties is a key management practice towards SDS. Since SDS severity is exacerbated by soybean cyst nematode infestation, varieties with dual resistance against both SDS and soybean cyst nematode may be needed.
