Population Dynamics and Survival of Xanthomonas campestris in Soil in Citrus Nurseries in Maryland and Argentina. J. H. Graham, Associate Professor, University of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred 33850. T. R. Gottwald, E. L. Civerolo, and R. G. McGuire. Research Plant Pathologist, U.S. Department of Agriculture, ARS, Orlando, FL 32803; Research Plant Pathologist, U.S. Department of Agriculture, ARS, Beltsville, MD 20705; and Assistant Research Scientist, University of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred 33850. Plant Dis. 73:423-427. Accepted for publication 27 December 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0423.

The population dynamics and survival in soil of nursery strains of Xanthomonas campestris causing citrus bacterial spot in Florida (Xc) and strains of X. c. pv. citri causing Asiatic citrus canker (Xcc-A) were evaluated in citrus nurseries under quarantine in Maryland and in Argentina, where citrus canker is endemic. In Maryland, Xc and Xcc-A were recovered from the soil under infected nursery seedlings of Swingle citrumelo when the soil was relatively moist (Ψ ≥ –30 cbar) but not when it was drier (Ψ < –100 cbar). The pathogens were not detected on leaves of adjacent uninfected trees or in the soil under them. The populations of Xc and Xcc-A were generally lower in soil than on leaves with lesions and on symptomless leaves from diseased plants. In Argentina, Xcc-A was detected in a sandy soil in grapefruit and sweet orange nurseries with disease proportions of 0.97 and 0.89, respectively. Fluctuations in soil populations were correlated with rainfall, soil moisture, and air temperature, as well as leaf populations. After the removal of infested plants to simulate eradication, Xcc-A could not be recovered after 21 days from either nursery site. It appears that Xcc-A and Xc have very limited survival capability in subtropical soils.

Keyword(s): environmental effects.