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Physiology and Biochemistry

Physiological and Pathological Characteristics of Virulent and Avirulent Strains of the Bacterium that Causes Pierce?s Disease of Grapevine. D. L. Hopkins, Professor of plant pathology, University of Florida, Agricultural Research and Education Center, Leesburg 32749-0388; Phytopathology 75:713-717. Accepted for publication 26 December 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-713.

Virulence of strains of Pierce?s disease bacteria to grapevine (Vitis vinifera ?Carignane?) was determined by the multiplication of bacteria in the xylem vessels of inoculated petioles or stem internodes and by their capability to move systemically from vessel to vessel through the plant. Virulent strains reached populations of 10⁶?10⁷ colony-forming units per centimeter of inoculated petiole and avirulent strains reached only 10⁴?10⁵ colony-forming units per centimeter. Virulent strains moved systemically from the inoculated internode and infested xylem vessels in all but the youngest grapevine tissue within 3 mo. Avirulent strains did not move beyond the inoculated internode. Weakly virulent strains multiplied more slowly in petioles than virulent ones but eventually reached 10⁶ colony-forming units per centimeter, and systemic movement of weakly virulent strains was slower. None of the strains that cause Pierce?s disease produced pectolytic, cellulolytic, or proteolytic enzymes in culture. Peroxidase and lysophospholipase were produced; virulent strains produced the most lysophospholipase.