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Subterranean Clover Distortion: A New Viruslike Disease with Unusual Characteristics. Katie Helms, Division of Plant Industry, Commonwealth Scientific and Industrial Research Organisation, Canberra, A.C.T. 2601, Australia. P. W. G. Chu, and R. R. Martin. Division of Plant Industry, Commonwealth Scientific and Industrial Research Organisation, Canberra, A.C.T. 2601, Australia, and Agriculture Canada, Vancouver, British Columbia, V6T 1X2, Canada. Plant Dis. 76:420-425. Accepted for publication 11 July 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0420.

A new mechanically transmissible viruslike disease, subterranean clover distortion, was found in subterranean clover (Trifolium subterraneum) in a pasture in New South Wales. The pathogen has a wide experimental host range. Symptoms varied from thickening and distortion of young leaves, reddening of older leaves, and production of axillary shoots on subterranean clover to chlorosis of leaves, flower malformation, flower abortion, and stem necrosis on other hosts. Symptomless shoots often developed on infected plants. No local lesion host was identified. A disease-specific double-stranded RNA was isolated from tissues of infected subterranean clover, phlox, alfalfa, and broad bean plants with typical symptoms but not from tissues of healthy control plants or parts of inoculated plants that failed to show symptoms. The dsRNA was estimated to be 11-13 kbp (Mr 7.3-8.6 106). Three size classes of quasi-spherical particles (85-90, 66-70, and 50-55 nm in diameter) were detected in partially purified preparations. Electron microscopy indicated that the 85- to 90-nm and 66- to 70-nm particles possessed double membrane envelopes and single-walled membrane envelopes, respectively.