Spiroplasma citri in Maryland: Isolation from Field-Grown Plants of Horseradish (Armoracia rusticana) with Brittle Root Symptoms. Robert E. Davis, Plant Virology Laboratory, Plant Protection Institute, Agricultural Research Service, Beltsville Agricultural Research Center, Beltsville, MD 20705. Jacqueline Fletcher, Plant Pathology Department, University of Illinois at Urbana-Champaign, Urbana 61801. Plant Dis. 67:900-903. Accepted for publication 5 February 1983. 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, 1983. DOI: 10.1094/PD-67-900.

Horseradish plants with stunted young green leaves, extensive necrosis in old leaves, and a darkened phloem ring in roots were found in commercial horseradish fields in Maryland during September 1981. Spiroplasmas were consistently isolated in pure culture in vitro from surface-sterilized samples of roots from plants showing these symptoms. Results from serological tests of growth inhibition and enzyme-linked immunosorbent assay and from polyacrylamide gel electrophoretic analysis of cellular proteins indicated these spiroplasmas were strains of Spiroplasma citri, the cause of brittle root disease of horseradish in Illinois.