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A Nomenclature for Rhynchosporium secalis Pathotypes. S. B. Goodwin, Department of Genetics, University of California, Davis 95616, Present address: Department of Plant Pathology, 334 Plant Science, Cornell University, Ithaca, NY 14853; R. W. Allard(2), and R. K. Webster(3). (2)Department of Genetics, University of California, Davis 95616; (3)Department of Plant Pathology, University of California, Davis 95616. Phytopathology 80:1330-1336. Accepted for publication 5 June 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-1330.

A ?standard? nomenclature based on octal numbers was developed for naming pathotypes of the barley scald fungus, Rhynchosporium secalis. Twenty-four barley differential cultivars were included in this nomenclature. These cultivars were chosen for nomenclatural purposes because they have been the most commonly used in previous studies, and because jointly they carry all of the known genes for scald resistance. The octal nomenclature allows a unique appellation to be generated for each possible combination of pathogenicities in the fungus; and, because only eight different patterns must be learned, this system can be quickly and easily applied by those not familiar with it. Cultivars with related resistance genes were grouped, so far as possible, in the same octal digits because this simplifies genetic interpretation of the names obtained. In this way, the results from studies by different investigators who do not use the same differentials can be compared easily. Use of the octal nomenclature developed in this study mitigates the barriers to comparisons among studies caused by previous nomenclatures.