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Dynamics and Spatial Distribution of Xanthomonas campestris pv. citri Group E Strains in Simulated Nursery and New Grove Situations. T. R. Gottwald, Research Plant Pathologist, U.S. Department of Agriculture, ARS, Orlando, FL. E. L. Civerolo, S. M. Garnsey, R. H. Brlansky, J. H. Graham, and D. W. Gabriel. Research Plant Pathologist, U.S. Department of Agriculture, ARS, Beltsville, MD; Research Plant Pathologist, U.S. Department of Agriculture, ARS, Orlando, FL; Associate Professors, Citrus Education and Research Center, University of Florida, Lake Alfred; and Assistant Professor, Department of Plant Pathology, University of Florida, Gainesville. Plant Dis. 72:781-787. Accepted for publication 22 April 1988. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988. DOI: 10.1094/PD-72-0781.

The distribution and spread of strains of Xanthomonas campestris pv. citri group E were studied on Duncan grapefruit and Valencia orange in two nursery plots and two new grove plots, one each of the same cultivars at Frederick, MD, under strict security. Strains of X. c. pv. citri group E have been reported only in Florida and primarily on young citrus stock. Focal plants inoculated with Florida strains of X. c. pv. citri group E were placed in the center of each of the four plots. Epiphytic bacterial populations were detected 3 m from foci by days 49 and 79 in the two nursery plots by immunofluorescence microscopy and/or DNA-DNA hybridization probe techniques. In new grove plots, bacteria were detected at the 13.8-m limits of the plots by day 50 by both detection techniques. Bacterial spread and eventual disease development appeared to be nondirectional. Disease symptoms developed in the grapefruit nursery and grapefruit new grove plots by days 94 and 141, respectively. Epiphytic foliar populations of X. c. pv. citri group E decreased in all plots in the fall and dropped further after frosts. X. campestris was repeatedly recovered from soil at 103104 cfu/g under the grapefruit nursery focal tree. Nonpathogenic X. campestris was recovered from under the orange and grapefruit nursery focal trees and the orange new grove focal tree. No X. c. pv. citri group E was detected in soil under asymptomatic plants. As temperatures decreased in the fall, X. campestris soil populations also decreased. Soil populations were not reduced further immediately following a freeze.