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Isozyme Comparisons of Septoria Isolates Associated with Citrus in Australia and the United States. M. R. Bonde, Research plant pathologist USDA, Agricultural Research Service, Foreign Disease-Weed Science Research, Ft. Detrick, Building 1301, Frederick, MD 21702; G. L. Peterson(2), R. W. Emmett(3), and J. A. Menge(4). (2)Biologist, USDA, Agricultural Research Service, Foreign Disease-Weed Science Research, Ft. Detrick, Building 1301, Frederick, MD 21702; (3)Senior plant pathologist, Department of Agriculture and Rural Affairs, Sunraysia Horticulture Research Institute, Australia; and (4)Professor of Plant Pathology, University of California, Riverside 92521-0122. Phytopathology 81:517-521. Accepted for publication 29 November 1990. 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, 1991. DOI: 10.1094/Phyto-81-517.

Septoria cultures isolated from citrus have sometimes been referred to in Australia as S. depressa and in the United States only as S. citri. However, it is not clear whether S. depressa and S. citri are the same or different species. To help determine the answer, isozymes of Septoria isolated from citrus in Australia and the United States were compared. Of 28 isolates studied (18 from Australia and 10 from the United States, spanning the observed morphological variation in each country) for 25 enzymes, only one isolate (AUS 335) from Australia was markedly different. The average coefficient of similarity comparing all possible pairs of isolates, except AUS 335, was 0.97, indicating little isozyme variation. Twenty-three of 25 enzymes had no detectable variation in these isolates. The average coefficient of similarity comparing AUS 335 to other isolates was 0.58. Based on the data, these isolates (except the aberrant isolate AUS 335) are of the same species.