Relatedness of Mycoplasmalike Organisms Associated with Ash Yellows and Lilac Witches’-Broom. C. R. Hibben, Brooklyn Botanic Garden Research Center, Ossining, NY 10562. W. A. Sinclair, R. E. Davis, and J. H. Alexander III. Department of Plant Pathology, Cornell University, Ithaca, NY 14853-5908; Microbiology and Plant Pathology Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705; and Arnold Arboretum of Harvard University, Jamaica Plain, MA 02130-3519. Plant Dis. 75:1227-1230. Accepted for publication 7 May 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-1227.

The mycoplasmal diseases ash yellows (AshY) and lilac witches’-broom (LWB) were diagnosed on the basis of symptoms and the DAPI (4’,6-diamidino-2-phenylindole·2HCl) fluorescence test in 12 taxa of Fraxinus and 35 taxa of Syringa, respectively, at the Arnold Arboretum, Jamaica Plain, MA. AshY and LWB also occurred together in other arboreta in the United States and Canada. Ash mycoplasmalike organisms (MLOs) were transmitted to lilacs, and lilac MLOs were transmitted to ash by dodder (Cuscuta spp.). Ash and lilac MLOs caused identical symptoms in ash, lilac, periwinkle (Catharanthus roseus), and carrot (Daucus carota). DNA from diseased lilac or ash from diverse locations and from periwinkle infected with AshY or LWB MLOs hybridized with a biotin-labeled cloned DNA probe that detects AshY MLOs specifically. DNA from healthy ash, lilac, or periwinkle or from periwinkle infected with two other plant MLOs did not hybridize with the AshY-specific probes. Thus, the lilac and ash MLOs are similar and possibly identical.