Bacterial Leaf Scorch of Northern Red Oak: Isolation, Cultivation, and Pathogenicity of a Xylem-Limited Bacterium. C. J. Chang, Department of Plant Pathology, University of Georgia, Georgia Station, Griffin 30223-1797. J. T. Walker, Department of Plant Pathology, University of Georgia, Georgia Station, Griffin 30223-1797. Plant Dis. 72:730-733. Accepted for publication 6 May 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0730.

A xylem-limited bacterium associated with scorch in northern red oak (Quercus rubra) was consistently isolated and cultured on CS20 medium from August 1982 through January 1983 and from August 1983 through December 1983. The colonies were opalescent white and reached 0.04–0.07 mm in diameter in 2 wk. All triple-cloned isolates failed to grow on nutrient agar, 523, and YDC medium. No colonies developed from sap of symptomless trees. The cells of the leaf scorch bacterium were rod-shaped, measured 0.4–0.75 × 1.05–3.5 ?m, and had rippled walls. The cells appeared to divide by binary fission. In double-diffusion serological tests, the bacterium from oak was partially related to the Pierce’s disease bacterium but was not related to the phony peach bacterium. Fifty percent of red oak seedlings artificially inoculated with triple-cloned isolates from scorched oak developed scorch, and the bacterium was reisolated from them. Control seedlings inoculated with phosphate-buffered saline remained symptomless, and their xylem yielded no bacteria on CS20 medium.