CHARACTERIZATION OF MYCOPLASMALIKE ORGANISMS FROM FRAXINUS, SYRINGA, AND ASSOCIATED PLANTS FROM GEOGRAPHICALLY DIVERSE SITES

Mycoplasmalike organisms (MLOs) in six species of ash (Fraxinus) and lilac (Syringa) at 13 locations from southern Quebec and Massachusetts to Zion National Park, Utah, were detected by the DAPI (4'-6-diamidino-2-phenylindole-2HCl) fluorescence test. Relatedness of these MLOs to one another was established through dot hybridization of DNA samples from diseased plants with four ash yellows (AshY)-specific DNA probes and through immunofluorescence microscopy with an AshY-specific monoclonal antibody. In a search for possible alternative plant hosts of the AshY agent, the DAPI test was utilized to detect MLOs in 13 other species growing in the vicinity of diseased ash in central New York State and in two species in Zion National Park. These species were (asterisks indicate first record of microscopic detection of MLOs) *Apocynum cannabinum, *Asclepias syriaca, Aster novae-angliae, *Carya cordiformis, *Cornus racemosa, *Chrysopsis villosa, *Chrysothamnus nauseosus, *Epilobium ciliatum, *Lotus corniculatus, Prunus virginiana, Salix sp., *Solidago rugosa, and *Spiraea tomentosa. With the exception of P. virginiana, which contained an X-disease MLO, none of these species was found to be diseased at more than three of the 24 sites of AshY occurrence that were surveyed. Diseased phloem of 10 of these species was tested with the AshY-specific monoclonal antibody and did not react with it. A 1.2-kb fragment of DNA of the 16S ribosomal RNA gene was amplified by polymerase chain reaction from each of four MLO strains from ash and lilac, one strain each from A. syriaca, C. racemosa, S. rugosa, and S. tomentosa, and three reference strains from other sources, maintained in periwinkle (Catharanthus roseus). Restriction fragments obtained by digestion of the amplified products with enzymes AluI, KpnI, and MseI were similar for the ash and lilac MLOs and differentiated them from the others tested. The MLOs detected in A. novae-angliae, C. racemosa, and L. corniculatus were related to members of the aster yellows MLO group on the basis of reaction with an aster yellows-specific monoclonal antibody. This finding for C. racemosa was supported by results of restriction enzyme analysis of the 16S ribosomal DNA fragment. To date, Syringa spp. are the only known alternative hosts of AshY MLOs.