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Etiology

Pathological, Restriction-Fragment Length Polymorphism, and Fatty Acid Profile Relationships Between Xanthomonas campestris from Citrus and Noncitrus Hosts. J. H. Graham, Associate professor, University of Florida, IFAS, Citrus Research and Education Center, Lake Alfred 33850; J. S. Hartung(2), R. E. Stall(3), and A. R. Chase(4). (2)Research plant pathologist, U.S. Department of Agriculture, ARS, Plant Science Institute, Beltsville, MD 20705; (3)Professor, University of Florida, IFAS, Department of Plant Pathology, Gainesville 32611; (4)Professor, University of Florida, IFAS, Central Florida Research and Education Center, Apopka, 32703. Phytopathology 80:829-836. Accepted for publication 16 February 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-829.

Pathogenic strains of Xanthomonas campestris from noncitrus hosts were screened for their ability to cause necrosis on wounded, detached leaves of the citrus cultivars Swingle citrumelo and Duncan grapefruit. Thirteen of 56 noncitrus strains produced reactions that were similar to those caused by X. c. pv. citrumelo strains isolated from several outbreaks of citrus bacterial spot in Florida nurseries. Noncitrus strains of the weakly to moderately aggressive type, including strains of X. c. pv. alfalfae, X. c. pv. fici, X. c. pv. maculifoliigardeniae, and three strains from Strelitzia, elicited necrotic spots on spray-inoculated immature foliage of both Swingle citrumelo and Duncan grapefruit. When noncitrus strains were injection-infiltrated into Swingle citrumelo leaves, they multiplied and reached populations as high as those attained by a weakly aggressive strain from citrus. Strains of X. c. pv. campestris, X. c. pv. phaseoli, and X. c. pv. malvacearum that did not elicit necrosis on detached leaves failed to multiply in leaves. The group of weakly to moderately aggressive strains from noncitrus hosts was compared with aggressive and less aggressive strains from citrus by restriction-fragment length polymorphism analysis of genomic DNA and by cellular fatty-acid profiles. Most of the weakly to moderately aggressive strains of noncitrus origin could not be separated from the group of citrus strains by either analysis. Other X. campestris strains that did not grow in planta and give a disease reaction were less related to the citrus and the other noncitrus strains by these analyses. These findings raise doubts as to the role of less aggressive strains as primary pathogens of citrus and their inclusion within a separate pathovar, X. c. pv. citrumelo.