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Validating Immunoassay Test Performance in the Detection of Corynebacterium sepedonicum During the Growing Season. Neil C. Gudmestad, Department of Plant Pathology, North Dakota State University, Fargo 58105; Debra Baer(2), and Chester J. Kurowski(3). (2)(3)Department of Plant Pathology, North Dakota State University, Fargo 58105, (3)Present address: Harris Moran Seed Co., 100 Breen Road, San Juan Bautista, CA 95045 Phytopathology 81:475-480. Accepted for publication 31 December 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-475.

The growth and serological detection of Corynebacterium sepedonicum in potato stems was studied in the growth chamber and in the field. Populations of C. sepedonicum were similar in two susceptible cultivars, Norchip and Russet Burbank, which differ in seasonal maturity. The maximum population of the ring rot bacterium in these cultivars was between 108 and 109 cfu/g fresh weight, depending on the growing season. Populations of C. sepedonicum in stems of field-grown plants of Belrus developed more slowly and were generally lower when compared to the two susceptible cultivars. Development of bacterial ring rot symptoms in Norchip and Russet Burbank was associated with bacterial populations ?107 cfu/g fresh weight. Indirect fluorescent antibody staining (IFAS) and enzyme-linked immunosorbent assay (ELISA) were studied for their effectiveness in detecting populations of C. sepedonicum during the growing season. Specificity and efficiency of both serological tests were high, >94% and >90%, respectively, in both years of the study. IFAS and ELISA were capable of detecting 106 cfu/g fresh weight with a detection sensitivity of approximately 80%. Based on the development of populations of C. sepedonicum in planta and the overall efficiency of IFAS and ELISA, these serological tests could be used to detect symptomless ring rot infections during the growing season.

Additional keywords: Clavibacter michiganense subsp. sepedonicum, Solanum tuberosum.