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Molecular Plant Pathology

Characterization of Double-Stranded RNA in Isolates of Phytophthora infestans from Mexico, the Netherlands, and Peru. Joseph R. Newhouse, Research plant pathologists, U.S. Department of Agriculture, Agricultural Research Service, Foreign Disease-Weed Science Research Unit, Ft. Detrick—Bldg. 1301, Frederick, MD 21702; Paul W. Tooley(2), Oney P. Smith(3), and Richard A. Fishel(4). (2)(3)Research plant pathologists, U.S. Department of Agriculture, Agricultural Research Service, Foreign Disease-Weed Science Research Unit, Ft. Detrick—Bldg. 1301, Frederick, MD 21702; (4)Group leader, genetic recombination and repair, Laboratory of Chromosome Biology, National Cancer Institute, Frederick Cancer Research Facility, Ft. Detrick. Phytopathology 82:164-169. Accepted for publication 24 August 1991. 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, 1992. DOI: 10.1094/Phyto-82-164.

Seventy-nine isolates of Phytophthora infestans, from Mexico, the Netherlands, Peru, Israel, and the United States, were screened for the incidence of double-stranded (ds) RNA. The dsRNA was most abundant in Mexican isolates (83.3%), followed by isolates from the Netherlands (20%) and Peru (2.9%). P. infestans isolates from Israel and the United States were dsRNA-free. Double-stranded RNA was found in both A1 and A2 mating-type Mexican isolates, while only A2 mating-type isolates from the Netherlands contained dsRNA. Dutch and Peruvian isolates contained dsRNA segments that were identical in size with dsRNA segments recovered from Mexican isolates. In addition to the dsRNA segments and patterns previously reported in Mexican isolates, three new segments and six new patterns were discovered. The dsRNAs ranged in size from 1.35 to 11.10 kbp, and transmission electron microscopy of the dsRNA revealed linear molecules. Northern blot hybridization analysis showed that sequence homology exists between comigrating dsRNA segments of Mexican, Dutch, and Peruvian isolates, and that at least four nonhomologous groups of dsRNA occur in P. infestans.