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Molecular Plant Pathology

Restriction Fragment Length Polymorphisms Distinguish Xanthomonas campestris Strains Isolated from Florida Citrus Nurseries from X. c. pv. citri. John S. Hartung, U.S. Department of Agriculture, Agricultural Research Service, Plant Science Institute, Fruit Laboratory, Beltsville, MD 20705; E. L. Civerolo, U.S. Department of Agriculture, Agricultural Research Service, Plant Science Institute, Fruit Laboratory, Beltsville, MD 20705. Phytopathology 79:793-799. Accepted for publication 24 February 1989. 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, 1989. DOI: 10.1094/Phyto-79-793.

Genomic DNA prepared from 21 strains of Xanthomonas campestris pv. citri, 14 strains of X. campestris isolated from Florida citrus nurseries, and 10 strains of five other pathovars of X. campestris was used for restriction fragment length polymorphism (RFLP) analysis. The X. c. citri strains included 14 strains from group A, five strains from group B, and single strains from groups C and D. Seven cosmid clones selected from a library of strain XC62 of X. c. citri (group A) were used to screen for EcoRI and PvuII polymorphisms, which were quantified by calculating coefficients of similarity (F). Statistical analysis of the RFLP data distinguished the group A strains from the other strains of X. c. citri, which formed a second distinct group (group B/C/D). On the basis of these analyses, a clonal population structure is evident for this globally distributed pathogen, consistent with previous groupings of the strains based on other criteria. A relatively heterogeneous group of related strains of X. campestris has been isolated from Florida citrus nurseries. Statistical analysis of the RFLP data revealed a significant separation between the 14 strains of X. campestris isolated from Florida citrus nurseries and all strains of X. c. citri. Thus, this collection of strains is not closely related to previously recognized strains of X. c. citri. This is consistent with disease symptomology, epidemiology, and distribution. We conclude that the disease associated with X. campestris in Florida citrus nurseries is not a form of citrus bacterial canker and that the pathogen is not a strain of X. c. citri.