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Association of a Rickettsialike Organism with Pierce’s Disease of Grapevines and Alfalfa Dwarf and Heat Therapy of the Disease in Grapevines. A. C. Goheen, Research Plant Pathologist, Plant Science Research Division, USDA, Department of Plant Pathology, University of California, Davis 95616; G. Nyland(2), and S. K. Lowe(3). (2)(3)Professor of Plant Pathology, and Staff Research Associate IV, respectively, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 63:341-345. Accepted for publication 3 October 1972. DOI: 10.1094/Phyto-63-341.

Ultrathin sections of grapevines affected with Pierce’s disease and alfalfa plants affected with dwarf showed rickettsialike organisms in the lumen and between the vessels of the xylem tissues when examined with an electron microscope. They were not present in sections from healthy grapevines until such vines were inoculated by exposure to infective leafhoppers. The organisms had cell walls, cytoplasmic membranes, and a cytoplasm with electron-dense organelles. They measured ca. 0.4 µ in diam and up to 3.2 µ in length. The cell wall, of several layers, was rippled, much like the cell walls of other rickettsiae known in animal hosts. The organisms could not be cultured on an artificial medium. Grapevines were freed of the causal agent of Pierce’s disease by immersion of the entire plant in water at 45 C for 180 min, 50 C for 20 min, or 55 C for 10 min. The vines tolerated immersion at 45 C for 24 hr, 50 C for 2.5 hr, and 55 C for 10 min. Plants freed of the causal agent remained healthy. Such plants were susceptible to the disease when reinoculated by infective leafhopper vectors.

Additional keywords: Hordnia circellata, bacterial disease.