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Isolation and Cloning of DNA Fragments from a Mycoplasmalike Organism Associated with Walnut Witches’-Broom Disease. J. Chen, Department of Plant Pathology, University of Georgia, Griffin 30223; C. J. Chang(2), R. Jarret(3), and N. Gawel(4). (2)Department of Plant Pathology, University of Georgia, Griffin 30223; (3)USDA, ARS, Department of Plant Introduction, 1109 Experiment St., Griffin, GA 30223; (4)Department of Horticulture, University of Georgia, Griffin 30223. Phytopathology 82:306-309. Accepted for publication 10 October 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-306.

Total DNA was extracted using CTAB buffer from freeze-dried leaves of mature walnut (Juglans nigra) showing severe symptoms of walnut witches’-broom (WWB) disease. DNA of WWB mycoplasmalike organism (MLO) was separated from host DNA by CsCl/bisbenzimide gradient centrifugation. A genomic library was constructed from MLO DNA that contained either chromosomal or extrachromosomal DNA fragments. Extrachromosomal DNA probes hybridized to DNA from WWB and pecan bunch (PB) tissues, but not to DNA from periwinkle (Catharanthus roseus) infected with western X (WX), eastern aster yellows (EAY), and western severe aster yellows (WSAY) MLOs, beet leafhopper-transmitted virescence agent (BLTVA), or Spiroplasma citri (SC). Chromosomal DNA probes hybridized to DNA from tissues infected by MLOs associated with WX, WSAY, or BLTVA, but not PB, EAY, or SC.