Last year we began testing soybean varieties for tolerance to sudden death syndrome (SDS). Funded by checkoff dollars, we have repeated the test this year with varieties submitted to us by private companies.

The SDS tolerance test was conducted in a field near Ames, Iowa. To ensure uniform and consistent disease pressure across plots, we planted dry oats infested with the SDS pathogen along with the soybean seed. Our field experiments show this method, developed by our project at Iowa State University, can provide a consistent level of disease pressure. Details of this method are available upon inquiry.

Lines were planted in plots consisting of two 10-foot-long rows at eight seeds per foot with a row spacing of 30 inches. Lines were replicated three times. Plots were evaluated in early September and each line was given a numerical tolerance score from 0 to 10 based on leaf symptoms, with 10 indicating 100% defoliation. Low scores indicate a high level of tolerance. Most entries in our tests are tolerant to this disease.

Disease pressure this year was less than that of 1999 due to dry conditions in late summer and in general, yields were poor. Varieties with ratings of 3 or 4 show some level of susceptibility to the disease compared with susceptible controls. If you want to compare this year-s results with those in 1999, information can be found in November 8, 1999, ICM newsletter [1].

SDS Tolerance Test 2000