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Phenotypic Changes in Populations of Phytophthora infestans from Eastern Germany. S. S. Daggett,Department of Biology, The Pennsylvania State University, University Park 16802; E. Götz(2), and C. D. Therrien(3). (2)Institute for Potato Research, Gross Lüsewitz 2551, Germany; (3)Departments of Biology and Plant Pathology, The Pennsylvania State University, University Park. Phytopathology 83:319-323. Accepted for publication 15 December 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-319.

A total of 106 isolates of Phytophthora infestans collected in eastern Germany between 1976 and 1990 was analyzed for mating type, allozyme phenotype, and response to metalaxyl. The A2 mating type was found among isolates collected in 1980. Although an increase in the frequency of the A2 mating type has been observed since 1976, it did not increase to a frequency of 0.5, which is found in Mexico. Metalaxyl resistance was first observed among isolates collected in 1977, prior to the commercial use of the fungicide in eastern Germany. Between 1976 and 1990 the frequency of isolates resistant within a sample to metalaxyl increased from 0 to 40%. The number of isolates within a sample exhibiting an intermediate response to metalaxyl fluctuated from year to year. Prior to 1984 all A1 isolates, except one, had the dilocus allozyme phenotype Gpi-1 (glucose phosphate isomerase) 86/100, Pep-1 (peptidase) 92/100. A2 mating type isolates were 100/100 for Gpi-1 and either 100/100 or 92/100 for Pep-1. The predominant dilocus phenotype for isolates collected from 1984 to 1988 was 100/100 for both Gpi-1 and Pep-1. Two new phenotypes, Pep-1 83/100 and Gpi-1 90/100, appeared in the population in 1987 and 1990, respectively. By 1990, the frequency of Pep-1 83/100 isolates had increased to 26%. The remainder of the 1990 isolates were 100/100 for Pep-1. Eighty-eight percent of the isolates collected in 1990 were 100/100 for Gpi-1. The remaining 12% were 90/100. The changes in phenotypes observed in the eastern German population were similar to those being observed elsewhere.