Relative Resistances of Potato Clones in Response to New and Old Populations of Phytophthora infestans. D. A. Inglis, Washington State University-Mount Vernon Research and Extension Unit, 1468 Memorial Highway, Mount Vernon 98273. D. A. Johnson, Department of Plant Pathology, Washington State University, Pullman 99164-6430; D. E. Legard and W. E. Fry, Department of Plant Pathology, Cornell University, Ithaca, NY 14853; and P. B. Hamm, Hermiston Agricultural Research and Extension Center, Department of Botany and Plant Pathology, Oregon State University, Hermiston 97838. Plant Dis. 80:575. Accepted for publication 5 February 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0575.

Potato cultivars and clones were evaluated in Washington and New York in 1993 and 1994 for field reaction to recent immigrant genotypes of Phytophthora infestans. Plants were visually evaluated at regular intervals for percent blighted foliage. Relative cultivar susceptibilities were compared by ranking the values obtained for areas under disease progress curves (AUDPC) of each line tested. Cultivar rankings in response to infection by new, immigrant isolates of P. infestans were nearly identical to rankings obtained previously with isolates prevalent prior to 1990. The cultivars Norchip, Hilite, Russet Norkotah, Goldrush, Superior, and Shepody were more susceptible than Russet Burbank. White Rose and Ranger Russet were similar in susceptibility to Russet Burbank. CO08-3008-1, ND-2438-7R, Kennebec, and Elba were less susceptible than Russet Burbank. Comparisons of the number of blighted tubers at harvest showed that foliage and tuber susceptibilities differed among cultivars. Shepody and Russet Norkotah tubers were most susceptible to tuber blight of those tested.