Cloning of Chromosomal and Extrachromosomal DNA of the Mycoplasmalike Organism That Causes Maize Bushy Stunt Disease. Michael J. Davis. Fort Lauderdale Research and Education Center, University of Florida, Institute of Food and Agricultural Sciences, 3205 College Avenue, Fort Lauderdale 33314 U.S.A.. James H. Tsai, Rebecca L. Cox, Larry L. McDaniel, and Nigel A. Harrison. Fort Lauderdale Research and Education Center, University of Florida, Institute of Food and Agricultural Sciences, 3205 College Avenue, Fort Lauderdale 33314 U.S.A.. MPMI 1:295-302. Accepted 27 October 1988. Copyright 1988 The American Phytopathological Society.

A Florida isolate of the mycoplasmalike organism (MLO) presumed to incite maize bushy stunt disease was extracted and partially purified from groups of the leafhopper vector, Dalbulus maidis, by using differential centrifugation, filtration, and discontinuous Percoll density gradient centrifugation. DNA was isolated from the MLO-enriched preparation and digested with Sau3A. Restriction fragments of MLO-associated DNA were ligated into the plasmid vector, pUC8, and cloned in Escherichia coli, strain TB1. Dot-, Southern-, and leafhopper-blot hybridizations identified 11 recombinant plasmids that contained either chromosomal or extrachromosmal MLO-associated DNA. These plasmids hybridized to DNA associated with the maize bushy stunt MLO in extracts from infected corn and from individual infected leafhoppers but not to DNA from either noninfected corn or leafhoppers. One of these recombinant plasmids also hybridized with DNA from Spiroplasma kunkelii, the pathogen causing corn stunt disease. Southern-blot analysis established that extrachromosomal DNA was associated with two MLO isolates from Florida and Mexico but not with an isolate from Texas.