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First Report of Potential Biological Control of Potato Spindle Tuber Viroid Disease by Virus-Satellite Combination. M. S. Montasser, Department of Botany, University of Maryland, College Park 20742-5815. J. M. Kaper, and R. A. Owens. USDA-ARS, Microbiology and Plant Pathology Laboratory, Beltsville, MD 20705. Plant Dis. 75:319. Accepted for publication 25 October 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0319E.

In greenhouse trials, tomato (Lycopersicon esculentum Mill. 'UC82B') plants inoculated with a combination of total viral RNA extracted from cucumber mosaic virus strain S (CMV-S) carrying the nonnecrogenic viral satellite CARNA-5 (CMV-associated RNA 5) and a severe strain of potato spindle tuber viroid (PSTV) showed much milder symptoms of PSTV infection than plants inoculated with PSTV alone. Plants preinoculated with total RNA extracted from CMV-S and then challenge-inoculated 8 or 16 days later with the severe strain of PSTV, which causes severe stunting and foliage distortion in tomato, showed very mild symptoms. Dot blots, polyacrylamide gel electrophoresis, and northern hybridization analyses showed reduced levels of viroid RNA accumulation. Levels of single- and double-stranded CARN A-5 in total nucleic acid extracts from tissue samples randomly collected from tested plants were unchanged when compared with the controls. This is the first report of a virus/satellite-viroid interaction (interference) that protects plants against disease.