DNA Hybridization Between Western Aster Yellows Mycoplasmalike Organism Plasmids and Extrachromosomal DNA from Other Plant Pathogenic Mycoplasmalike Organisms. Cheryl R. Kuske. Department of Plant Pathology, University of California, Davis 95616 U.S.A. Bruce C. Kirkpatrick, Michael J. Davis, and Erich Seemüller. Department of Plant Pathology, University of California, Davis 95616 U.S.A. MPMI 4:75-80. Accepted 26 September 1990. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society. 1991.

Native, ³²P-labeled plasmids isolated from the severe strain (SAY) of western aster yellows mycoplasmalike organism (MLO) or a cloned, 4.9-kb SAY plasmid fragment were used to probe Southern blots of undigested DNA isolated from plants infected with plant pathogenic MLOs from diverse geographic regions. SAY plasmid DNA hybridized with small extrachromosomal DNA molecules present in several virescence-inducing MLOs and the maize bushy stunt MLO (MBS), but not with DNA from decline-inducing MLOs or spiroplasmas. A cloned, 4.4-kb fragment of MBS extrachromosomal DNA hybridized with the plasmids present in six strains of western AY, and some, but not all of the virescence agents that hybridized with SAY probes. Sizes and numbers of extrachromosomal DNA molecules varied among MLO strains. No hybridization occurred with healthy plant or leafhopper DNA using either the SAY or MBS plasmid probes. The presence of homologous sequences between extrachromosomal DNAs of MLOs suggests they may contain similar genes or regulatory sequences.