Screening Soybean Varieties For Resistance
To SDS In the Field

Glen Hartman
USDA-ARS and Associate Professor Department of Crop Sciences
(217) 244-3258; ghartman@illinois.edu

Darin Eastburn
Associate Professor
Department of Crop Sciences
(217) 244-9632; eastburn@illinois.edu

Each year, soybean breeders and plant pathologists try to get ratings on the level of resistance to sudden death syndrome (SDS) for both breeding lines and commercial varieties. Unfortunately, most fields have very uneven distribution of SDS, so one plot may have severe SDS while a second plot has no disease. This makes it very difficult to identify the lines with the highest level of resistance.

We often have trials in fields that have a history of SDS but get very few symptoms. Currently, we are evaluating a number of inoculation methods in an attempt to get consistent disease ratings. The first method involves growing the fungus on sterilized sorghum seed and incorporating the seed into the upper 4 to 6 inches of soil prior to planting. This takes 400 to 500 pounds of infested sorghum per acre and takes a lot of labor to produce the inoculum. We generally get SDS symptoms in seedling stage, but we may not get any foliar symptoms later in the season.

Figure 1. Strip till unit.

Figure 2. Leaf symptoms of sudden death syndrome.

We know that the development of SDS is affected by soil moisture, soil compaction, and planting date. This year, we tried compacting the soil by driving over the entire field with a heavy tractor and then inoculating and planting. We also have added irrigation to be sure the pathogen is able to infect the soybean plant. In 2002, we also are inoculating with a slurry suspension containing the pathogen using a modified strip-till applicator. The slurry is injected approximately 6 inches in the ground, and the soybean varieties are planted above the inoculum. This method is very fast and can be used for large research plots.

Several other factors appear to affect SDS, but our main goal is to develop an inoculation method for screening breeding lines and soybean varieties.