APS Abstracts of Presentations

Field trials of South Dakota soybean varieties for susceptibility to northern stem canker. T. E. CHASE. Plant Science Department, South Dakota State University, Brookings. Phytopathology 93:S15. Publication no. P-2003-0108-AMA.

Pathogenicity of Diaporthe phaseolorum var. caulivora (DPC) isolates was assessed in 2001. Plots were inoculated at the R3-R5 stage by insertion of DPC-infested toothpicks into soybean (Glycine max) stems. Canker development was rapid and resulted in girdling lesions and wilting within three weeks, typical of northern stem canker. Controls inoculated with sterile toothpicks showed no symptoms. Infection efficiency ranged from 32% to 85% among the five test isolates. The most pathogenic isolate (DP00-126) was used to screen soybean varieties entered into SDSU crop performance testing (CPT) trials in 2002. Varieties within maturity groups 0, I and II (including conventional and glyphosate-resistant) were inoculated (ten stems each plus two checks). Within conventional groups, 50%-76% of varieties were susceptible and within the glyphosate-resistant group, 24-32% of varieties were shown to be susceptible, although one group could not be assessed because of maturation effects. These results demonstrate a significant degree of susceptibility to northern stem canker in South Dakota adapted soybean germplasm.