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Molecular Plant Pathology

Homology of the Agent Associated with Dapple Apple Disease to Apple Scar Skin Viroid and Molecular Detection of These Viroids. A. Hadidi, National Plant Germplasm Quarantine Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Building 011A, Beltsville, MD 20705; C. Huang(2), R. W. Hammond(3), and J. Hashimoto(4). (2)National Plant Germplasm Quarantine Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Building 011A, Beltsville, MD 20705, Present address: Biological Laboratory, Xinjiang August 1st Agricultural College, Urumqi, Xinjiang, People's Republic of China; (3)Microbiology and Plant Pathology Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Building 011A, Beltsville, MD 20705; (4)National Institute of Animal Health, Tsukaba Science City, Yatabe, Ibaraki 305, Japan. Phytopathology 80:263-268. Accepted for publication 5 September 1989. 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, 1990. DOI: 10.1094/Phyto-80-263.

Gel electrophoresis coupled with molecular hybridization analyses using ³²P-labeled SP6-generated apple scar skin viroid (ASSV)-specific cRNA probes demonstrated that the pathogen associated with dapple apple disease is a viroid that is closely homologous to ASSV. Dapple apple viroid (DAV) consists of fewer than 359 nucleotides and is systemically distributed in apple seed, fruit, bark, leaf, and root tissues of infected apple trees. Molecular hybridization assays using ³²P-labeled ASSV cRNA probes have been developed and applied for the detection of DAV or ASSV in small amounts of infected apple tissue (0.2–2.0 g). These assays are accurate, easy to perform, and applicable for screening DAV or ASSV in imported apple cultivars. These viroids now can be positively identified from infected apple tissue in a few days instead of a few years by fruit symptoms on grafted woody indicators.