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

Mycoplasmalike organisms (MLOs) in six species of ash (Fraxinus) and l ilac (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 f rom diseased plants with four ash yellows (AshY)-specific DNA probes a nd through immunofluorescence microscopy with an AshY-specific monoclo nal antibody. In a search for possible alternative plant hosts of the AshY agent, the DAPI test was utilized to detect MLOs in 13 other spec ies growing in the vicinity of diseased ash in central New York State and in two species in Zion National Park. These species were (asterisk s indicate first record of microscopic detection of MLOs) Apocynum ca nnabinum, Asclepias syriaca, Aster novae-angliae, *Carya cordiformis, Cornus racemosa, *Chrysopsis villosa, *Chrysothamnus nauseosus, *Epi lobium ciliatum, Lotus corniculatus, Prunus virginiana, Salix sp., *S olidago rugosa, and Spiraea tomentosa. With the exception of P. virgi niana, which contained an X-disease MLO, none of these species was fou nd to be diseased at more than three of the 24 sites of AshY occurrenc e that were surveyed. Diseased phloem of 10 of these species was teste d 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 a nd lilac, one strain each from A. syriaca, C. racemosa, S. rugosa, and S. tomentosa, and three reference strains from other sources, maintai ned in periwinkle (Catharanthus roseus). Restriction fragments obtaine d by digestion of the amplified products with enzymes AluI, KpnI, and MseI were similar for the ash and lilac MLOs and differentiated them f rom the others tested. The MLOs detected in A. novae-angliae, C. racem osa, and L. corniculatus were related to members of the aster yellows MLO group on the basis of reaction with an aster yellows-specific mono clonal 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.