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Disease Detection and Losses

Determination of Population Densities of Corynebacterium sepedonicum in Potato Stems During the Growing Season. S. H. De Boer, Agriculture Canada Research Station, 6660 N. W. Marine Drive, Vancouver, B.C., Canada, V6T 1X2; M. McCann, Agriculture Canada Research Station, 6660 N. W. Marine Drive, Vancouver, B.C., Canada, V6T 1X2. Phytopathology 79:946-951. Accepted for publication 1 May 1989. Copyright 1989 Department of Agriculture. Government of Canada. DOI: 10.1094/Phyto-79-946.

Estimates of population densities of Corynebacterium sepedonicum in potato stems grown from inoculated seed tubers were made during the growing season with a quantitative immunofluorescence procedure. Population densities, calculated as immunofluorescing units per gram fresh weight (IFU/g), reached a maximum of 10⁸ to 10¹⁰ in the cultivars Red Pontiac, Russet Burbank, and Desiree grown in growth rooms and in field plots. The population density increased most rapidly in Red Pontiac during the growing season, and this cultivar also expressed the highest incidence of bacterial ring rot symptoms. Desiree generally did not develop symptoms and had the lowest bacterial population densities in the stems. Russet Burbank expressed moderate symptoms and developed variable population densities. Within 80 days after planting, C. sepedonicum could be detected in symptomless stems of all three cultivars by immunofluorescence with a cell wall-specific monoclonal antibody and by enzyme-linked immunosorbent assay with an extracellular polysaccharide-specific monoclonal antibody. The ELISA values were positively correlated (correlation coefficient = 0.85) with estimates of population densities.