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Evidence Suggesting Nonassociation of Mycoplasma With Pea Disease. R. O. Hampton, Research Plant Pathologist, Agricultural Research Service, U. S. Department of Agriculture, Oregon State University, Corvallis 97331; E. R. Florance(2), R. F. Whitcomb(3), and R. J. Seidler(4). (2)Assistant Professor, Department of Biology, Columbia Basin College, Kennewick, Washington 99336; (3)Research Entomologist, Agricultural Research Service, U. S. Department of Agriculture, Plant Protection Institute, Beltsville Research Center, Beltsville, Maryland 20705; (4)Associate Professor, Department of Microbiology, Oregon State University, Corvallis 97331. Phytopathology 66:1163-1168. Accepted for publication 30 March 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1163.

Sixty mycoplasma isolates, with uniform colony type, were derived from five of 31 experiments using diseased pea tissue extracts as inoculum. Five of these isolates were identified serologically as Mycoplasma gallisepticum. The DNA of isolate Y12-5P consisted of 34.8% guanine-cytosine base composition, was 92% homologous with that of M. gallisepticum reference isolate S6, and constituted a genome size of 4.3-4.6 × 108 daltons. Isolate Y12-5P was found to be highly pathogenic to turkeys, but not to plants. Two isolates produced growth responses at three temperatures comparable to those of M. gallisepticum reference strain, S6. Mycoplasmalike structures visualized in diseased pea cytoplasm by ultrathin section electron microscopy were probably vesicles of host-cell membranes enclosing cytoplasm, ribosomes, and DNA-like strands. These lines of evidence suggest that the etiology of the previously reported pea disease may have been viral, that M. gallisepticum isolates derived in these studies originated from animal rather than plant sources, and that these isolates were introduced repeatably by an unknown means in attempts to cultivate microorganisms from diseased plant tissues.

Additional keywords: isolation, pathogenicity, temperature optima, DNA homology, genome size, ultrastructural cytology.