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Measurement of Soybean Resistance to Stem Canker Caused by Diaporthe phaseolorum var. caulivora. B. L. Keeling, Research Plant Pathologist, USDA-ARS, Stoneville, MS 38776. . Plant Dis. 72:217-220. Accepted for publication 23 September 1987. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988. DOI: 10.1094/PD-72-0217.

Two inoculation techniques were used to determine the relative resistance of soybean (Glycine max) cultivars to stem canker caused by Diaporthe phaseolorum var. caulivora. Sixty-day-old field-grown plants were inoculated by inserting toothpicks infested with the pathogen through the stem below the apical meristem or by spraying the plants with a water suspension of ascospores. Cultivars were rated for resistance on the basis of internal stem lesion development 42 days after toothpick inoculation. Ten cultivars, listed in order of increasing relative resistance, were rated for symptom development: J77-339 (susceptible), Forrest, Bedford, Bragg, Semmes, Jeff, Braxton, Centennial, Hood, and Tracy (resistant). The relative susceptibility of cultivars based on lesion size after inoculation with ascospores was similar to that found with the toothpick inoculation method. Either of the inoculation techniques can be used to evaluate the relative resistance of cultivars and breeding lines to this disease.