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Detection of Double-Stranded RNA in Phytophthora infestans. P. W. Tooley, Research plant pathologist, U.S. Department of Agriculture, Agricultural Research Service, Foreign Disease–Weed Science Research, Ft. Detrick, Bldg. 1301, Frederick, MD 21701; A. D. Hewings(2), and K. F. Falkenstein(3). (2)Research plant pathologist, USDA-ARS and Department of Plant Pathology, University of Illinois, N-519 Turner Hall, 1102 S. Goodwin Ave., Urbana 61801; (3)Associate professor of biology, Hood College, Frederick, MD 21701. Phytopathology 79:470-474. Accepted for publication 10 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-79-470.

Total nucleic acids were isolated from mycelial mats of Phytophthora infestans grown in V-8-juice broth at 18 C in darkness, and double-stranded RNA (dsRNA) was selectively purified by Whatman CF-11 cellulose chromatography. Polyacrylamide gel electrophoresis (PAGE) indicated that dsRNA was present only in Mexican isolates of P. infestans, most of which originated in the Toluca region. Thirty-six percent (n = 40) of the Mexican isolates tested contained dsRNA, and three distinct PAGE profiles were observed. Sizes of dsRNAs of P. infestans were estimated at 2,750, 2,500, 1,600, and 1,500 base pairs. No dsRNA was detected in 20 isolates of P. infestans from diverse locations within the United States and Europe. Attempts to purify virus particles from isolates that contained dsRNA were unsuccessful. Isolates containing dsRNA showed a wide range in virulence and showed increased growth in V-8-juice broth compared with a group of randomly chosen dsRNA-free Mexican isolates. The presence of dsRNA in P. infestans provides a valuable new marker for genetic and epidemiological studies.

Additional keywords: mycovirus, potato late blight.