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Disease Note.

Transmission of a Citrus-Infecting Strain of Spiroplasma citri to Horseradish. D. A. Sullivan, USDA-ARS, Boyden Fruit and Vegetable Insects Laboratory, Riverside, CA 92521. G. N. Oldfield, C. E. Eastman, J. Fletcher, and D. J. Gumpf. USDA-ARS, Boyden Fruit and Vegetable Insects Laboratory, Riverside, CA 92521; Illinois Natural History Survey, Urbana, IL 61801; Department of Plant Pathology, Oklahoma State University, Stillwater 74078; and Department of Plant Pathology, University of California, Riverside 92521. Plant Dis. 71:469. Accepted for publication 6 February 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0469E.

Spiroplasma citri Saglio et al, the citrus stubborn disease agent, has been shown to be serologically and electrophoretically indistinguishable from the causal agent of brittle root disease of horseradish (Armoracia rusticana Gaertn., Mey. & Scherb.) (2). Our report documents for the first time transmission of an isolate obtained from naturally infected citrus to horseradish plants. Nine of nine plants, each exposed to 20 beet leafhoppers (Circulifer tenellus (Baker)) reared on turnip infected with S. citri, developed foliar symptoms, including chlorosis, bronzing of older leaves, asymmetrical development of leaves, wilting, and necrosis. Most of the diseased plants died within 2 mo. Root cross sections of inoculated plants revealed the darkened ring of tissue in the vascular region that is characteristic of brittle root. Spiroplasmas were readily cultured in a liquid C-3G medium (I) from symptomatic plants but not from controls.

References: (1) T. A. Chen and C. H. Liao. Science 188: 1015, 1975. (2) J. Fletcher et al. Phytopathology 71: 1073, 1981.