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Symptom Expression Enhanced and Low Concentrations of Potato Spindle Tuber Viroid Amplified in Tomato with High Light Intensity and Temperature. M. E. Grasmick, Department of Plant Pathology, University of Wisconsin, Madison 53706. S. A. Slack, Department of Plant Pathology, University of Wisconsin, Madison 53706. Plant Dis. 69:49-51. Accepted for publication 18 June 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-49.

Indicator plants (Lycopersicon esculentum ‘Rutgers’) inoculated with a mild (PSTV-MA) or severe (PSTV-S) strain of potato spindle tuber viroid (PSTV) were grown in the summer and winter under prescribed temperature and light regimes to determine optimum conditions for symptom expression and viroid multiplication. Pruning the indicator plants increased detection based on symptoms 1,000-fold to 2.8 ื 10–1 pg/ml initial inoculum of PSTV-S. Tomato plants inoculated with PSTV-MA and grown at high temperatures (24–39 C, diurnal fluctuation) and supplemented with sodium vapor lighting (650 μE m–2 s–1) developed distinct symptoms. In summer and winter, symptoms developed earlier and with lower inoculum concentrations for both PSTV strains with sodium vapor supplemental lighting than without lighting or with fluorescent supplemental lighting. When winter-grown indicator plants were supplemented with high-intensity sodium vapor lights and indexed by polyacrylamide gel electrophoresis, detection of PSTV-S was enhanced 10,000-fold to 5.6 ื 10–2 pg/ml compared with plants grown under fluorescent lighting (130 μE m–2 s–1). It is suggested that sodium vapor lights should be used throughout the year to enhance detection of mild and severe PSTV strains.