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