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Detection of Ash Yellows Mycoplasmalike Organisms in Different Tree Organs and in Chemically Preserved Specimens by a DNA Probe vs. DAPI. W. A. Sinclair, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. H. M. Griffiths, R. E. Davis, and I.-M. Lee. Department of Plant Pathology, Cornell University, Ithaca, NY 14853; Microbiology and Plant Pathology Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705. Plant Dis. 76:154-158. Accepted for publication 13 August 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0154.

DNA of mycoplasmalike organisms (MLOs) was detected by dot hybridizations with a biotin-labeled cloned DNA probe, pBB115, in samples obtained from each of six naturally infected mature white ash (Fraxinus americana) on each of 11 dates over 14 mo. Hybridization signals were most consistent and intense with samples from the innermost phloem at the trunk base, less so with samples from fine roots, and least so with samples from coarse roots (2–6 mm in diameter), twigs, or leaves. The DNA probe detected MLOs as consistently as the DAPI (4’,6-diamidino-2-phenylindole·2HCl) fluorescence test in white ash but not in velvet ash (F. velutina), in which MLO populations were lower. Plant tissues destined for DNA extraction were effectively preserved in 5% (w/v) aqueous borax or by drying at 42 C as possible alternatives to freezing.