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Pink Rot of Potato Caused by Phytophthora erythroseptica in Pennsylvania. B. J. Christ, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. S. H. Kim, and T. N. Olson. Plant Disease Diagnostic Laboratory, Pennsylvania Department of Agriculture, Harrisburg 17110. Plant Dis. 72:912. Accepted for publication 19 July 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0912D.

Pink rot symptoms were observed in tubers collected randomly from plants with no aboveground symptoms in several potato fields (17 ha) in Lehigh County, Pennsylvania, in 1987. Samples were examined before and after a period of heavy rainfall 7-8 September; the rot was enhanced after the rainfall. Isolations from a sample of potatoes (Solanum tuberosum L. 'Katahdin,) revealed the presence of Phytophthora erythroseptica Pethyb. The P. erythroseptica was isolated from the inner portion of infected tubers on pimaricin-hymexazol-based selective medium. Homothallic aphigynous, elongated antheridia were produced on V-8/200 agar, and contorted elliptical sporangia without protruding papillae were observed 24 hr after the young mycelial plugs were flooded with Chen-Zentmyer's solution. Koch's postulates were satisfied by inoculating tubers of cvs. Katahdin and Norchip with the isolate of P. erythroseptica and then reisolating from the tubers. The grower harvested only 35% of his crop. In 1984, tubers sampled from 8 ha of Norchip in Potter County, Pennsylvania, had pink rot symptoms and isolations revealed P. erythroseptica; Koch's postulates were not performed. These two reports indicate that P. erythroseptica may be present in Pennsylvania soils.