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Scanning Electron Microscopy of Pierce's Disease Bacterium in Petiolar Xylem of Grape Leaves. Greta E. Tyson, Head and laboratory technician, Electron Microscope Center, Drawer EM, Mississippi State University, Mississippi State 39762; B. J. Stojanovic(2), Richard F. Kuklinski(3), Tony J. DiVittorio(4), and Michael L. Sullivan(5). (3)(5)Laboratory technicians, respectively, Electron Microscope Center, Drawer EM, Mississippi State University, Mississippi State 39762; (2)(4)Laboratory head and graduate research assistant, respectively, A. B. McKay Food and Enology Laboratory, Drawer NH, Mississippi State University. Phytopathology 75:264-269. Accepted for publication 26 September 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-264.

Petioles from a healthy grapevine and a grapevine showing symptoms of Pierce's disease infection were examined by scanning electron microscopy. In petioles from the healthy control vine, the lumens of tracheary elements lacked bacteria and seldom had tyloses. In petioles of leaves from the diseased plant, both with and without marginal leaf burn, bacterial aggregates were found in tracheary elements, and tyloses were seen much more frequently than in control petioles. Bacteria within aggregates often were associated with small globules, and some complete plugs appeared to be comprised mainly of such globular material. The overall percentages of colonized and plugged elements in petioles of symptomless leaves from the diseased plant were less than in petioles of leaves with marginal leaf burn from the same plant, ie, 19.5 versus 22.5% colonized, and 5.8 versus 7.7% plugged. In most petioles from the diseased plant almost all of the vascular bundles contained some colonized tracheary elements. Calcium-containing crystals were found infrequently in tracheary elements of both control and diseased plants; there is no evidence that these xylar inclusions are related to Pierce's disease.

Additional keywords: calcium oxalate crystals, transmission electron microscopy, X-ray energy dispersive analysis.