Evaluation location: Illinois, United States
Four liters of a steam-treated soil mix (1:1 sand/soil) was placed in 50 x 35 x 10 cm flats. A template was used to make seven furrows 2 cm deep and 35 cm long, and 10 cm3 of sorghum seed infested with F. solani f. sp. glycines isolate Mont-1 was evenly distributed in each furrow. The inoculum was then covered with 2 cm of soil, and the template was reapplied to make a 0.5-cm-deep furrow directly over the inoculum. Soybean seed was added to each furrow and covered with another 2 cm of soil. Plants were then placed on a greenhouse bench and grown under a 16-h photoperiod. Plants were watered to saturation after planting and maintained at near field capacity throughout the study. Two to 4 weeks after inoculation, plants were rated for SDS foliar symptoms on 4 separate dates. Plots were rated if two or more seeds emerged. Five seeds per entry were planted in flats containing 20 entries and one check. The susceptible check was Great Lakes 3302, and the moderately resistant checks were PI 520733 and PI 567374 . The entire set was screened in nonreplicated subsets of 500 PIs. Entries that had a mean disease severity rating and an AUDPC value 1.0 standard deviation below the mean of the subset or were not significantly different from either of the MR checks were advanced to the second stage. The second stage (1,302 entries from stage one) was planted as a nonreplicated set. The entries that had a mean disease severity rating and an AUDPC value 1.0 standard deviation below the mean of the set were advanced to the third stage. For the third stage, 212 accessions from stage two were arranged in a RCBD with four replications. Of these 212 entries, 57 were repeated in the final stage. These 57 PIs had foliar symptoms that were not significantly different from the MR check PI 567374 in the third stage.