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Mating Type, Race Composition, Nuclear DNA Content, and Isozyme Analysis of Peruvian Isolates of Phytophthora infestans. P. W. Tooley, U.S. Department of Agriculture, Agricultural Research Service, Foreign Disease-Weed Science Research, Ft. Detrick Building 1301, Frederick, MD 21701; C. D. Therrien(2), and D. L. Ritch(3). (2)(3)Department of Biology and Department of Plant Pathology, The Pennsylvania State University, University Park, 16802. Phytopathology 79:478-481. Accepted for publication 28 November 1988. 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, 1989. DOI: 10.1094/Phyto-79-478.

Thirty-four isolates of Phytophthora infestans from potatoes growing in the Central Highlands of Peru were analyzed. All isolates were of the A1 mating type. Feulgen cytophotometry was used to measure the DNA content of individual zoospore nuclei. The distribution of DNA content in the Peruvian isolates was very similar to that previously observed in isolates from the United States and Europe. Races 0, 1, and 1, 5 were the most common among the Peruvian isolates, representing 33, 39, and 15% of the population, respectively. The Peruvian population was monomorphic and identical to Mexican, U.S., and European populations at 11 enzyme loci. At two polymorphic loci, Peruvian isolates showed phenotypic distributions very similar to those of U.S. and European isolates. In terms of isozymes and races, fewer phenotypes were observed among Peruvian isolates than among isolates from Mexico, the United States, or Europe. These results strongly suggest a common ancestry for Peruvian, U.S., and European populations of P. infestans.