Occurrence and Relatedness of Extrachromosomal DNAs in Plant Pathogenic Mycoplasmalike Organisms. B. Schneider. Biologische Bundesanstalt für Land- und Forstwirtschaft, D-6915 Dossenheim, Germany. R. Mäurer(1), C. Saillard(2), B. C. Kirkpatrick(3), and E. Seemüller(1). (1)Biologische Bundesanstalt für Land- und Forstwirtschaft, D-6915 Dossenheim, Germany; (2)Laboratoire de Biologie Cellulaire et Moléculaire, Institut National de la Recherche Agronomique, F-33883 Villenave d’Ornon, France; and (3)Department of Plant Pathology, University of California, Davis, CA 95616 U.S.A. MPMI 5:489-495. Accepted 24 July 1992. Copyright 1992 The American Phytopathological Society.

DNA from mycoplasmalike organisms (MLOs) of herbaceous and woody plants as well as of leafhopper vectors was examined for the occurrence and interrelatedness of extrachromosomal DNAs. When MLO DNA, purified by repeated CsCl-bisbenzimide density gradient centrifugation, was analyzed in agarose gels stained with ethidium bromide, variable numbers of extrachromosomal DNA bands were observed in most organisms. Southern blots of undigested total DNA from infected plants probed with cloned extrachromosomal DNA fragments from four different MLOs revealed extrachromosomal DNA in almost all of the MLO isolates examined, including those from woody plants. Detection of extrachromosomal DNAs was sometimes difficult because of its low relative amount and/or insufficient homology to the probes. The ranges of hybridization of the probes from the four organisms with the extrachromosomal DNAs of the MLOs examined were very different. Also, the banding patterns obtained with a given probe varied considerably. No close correlation between the hybridization results and the symptoms induced by the isolates in periwinkle was found.