Bacterial Exudation from Lesions of Asiatic Citrus Canker and Citrus Bacterial Spot. L. W. Timmer, Professor, University of Florida, Institute of Food and Agricultural Sciences (IFAS), Citrus Research and Education Center, Lake Alfred 33850. T. R. Gottwald, and S. E. Zitko. Research Plant Pathologist, U.S. Department of Agriculture, Agricultural Research Service, Orlando, FL 32803; and Biological Scientist II, University of Florida, IFAS, Citrus Research and Education Center, Lake Alfred 33850. Plant Dis. 75:192-195. Accepted for publication 31 July 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0192.

When water was added to wells surrounding young lesions of Asiatic citrus canker (caused by Xanthomonas campestris pv. citri) on detached, field-collected leaves of grapefruit, about 10⁴–10⁵ bacteria per milliliter were exuded immediately. Bacterial exudation into the water continued at high levels for 24 hr, and cumulative release ranged from 10⁵ to 10⁶ per lesion. Fewer bacteria were exuded and bacteria were exuded more slowly from old lesions than from young lesions. Bacterial exudation from lesions of citrus bacterial spot (CBS) produced by X. c. pv. citrumelo on grapefruit and Swingle citrumelo was substantially less than that from Asiatic citrus canker lesions. CBS lesions of the aggressive strain (F1) released more bacteria than those of the moderately aggressive (F6) and weakly aggressive (F100) strains, and exudation declined with all three strains as lesions aged. Lesions of Asiatic citrus canker and CBS lesions produced by the three strains in a dew chamber at 30 C exuded more than 10⁶ bacteria per milliliter into water in wells surrounding new lesions. Under these conducive conditions, exudation continued at high levels for 48 hr for most strains of the CBS pathogen. The inability of the CBS pathogen to spread under field conditions unless susceptible tissue is abundant, environmental conditions are favorable, and plants have been injured may in part be the result of low inoculum production and rapid decline in bacterial exudation as lesions age.