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Temporal and Spatial Spread of Citrus Canker Within Groves. E. Danůs, Graduate student, Department of Plant Pathology, University of Florida, Gainesville 32611; R. D. Berger(2), and R. E. Stall(3). (2)(3)Professors, respectively, Department of Plant Pathology, University of Florida, Gainesville 32611. Phytopathology 74:904-908. Accepted for publication 28 February 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-904.

The spread of citrus canker, which is caused by Xanthomonas campestris pv. citri, was studied in Argentina. Disease gradients were obtained by plotting the proportion of diseased trees in individual rows or subplots of grouped rows versus distances from inoculum sources. The Gompertz transformation was used to linearize the gradients when plotted versus log10 (distance). In the regression equation for the linearized disease gradients, the slope b ranged from - 0.2 to - 4.13. Incidence of disease increased faster near inoculum sources; thus, disease gradients became steeper with time. The increasing steepness of the gradients was evident 40 mo after an inoculum source had been eradicated. Slope values were approximately the same for four scion-rootstock combinations at a given value of the Y-intercept (a). However, a and b increased slower in time on a resistant scion-resistant rootstock combination. Foci were detected by doublet analysis. Primary spread of canker resulted in a distribution of diseased trees that was sparse, but with a gradient. Diseased trees were not aggregated in the early spread. The later secondary spread was limited, and the incidence of disease increased faster near the inoculum sources. Aggregation of diseased trees then occurred.

Additional keywords: Citrus deliciosa, C. limon, C. sinensis, C. unshiu, epidemiology, Poncirus trifoliata.