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Focus Expansion in Plant Disease. III: Two Experimental Examples. F. van den Bosch, Institute of Theoretical Biology, State University of Leiden, Groenhovenstraat 5, 2311 BT Leiden, The Netherlands; H. D. Frinking(2), J. A. J. Metz(3), and J. C. Zadoks(4). (2)(4)Laboratory of Phytopathology, Wageningen Agricultural University, P.O. Box 8025, 6700 EE, Wageningen, The Netherlands; (3)Institute of Theoretical Biology, State University of Leiden, Groenhovenstraat 5, 2311 BT Leiden, The Netherlands. Phytopathology 78:919-925. Accepted for publication 18 December 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-919.

Experiments on focus expansion and its underlying processes were performed with stripe rust (Puccinia striiformis) on wheat and downy mildew (Peronospora farinosa) on spinach. Models for the spore production by an individual lesion as a function of time after victimization (the time kernel) and the spatial distribution of daughter lesions around one mother lesion (the contact distribution) were fitted to experimental data. Two methods to estimate the gross reproduction of the pathogen are described. Velocities of focus expansion were estimated using field observations from artificially established foci. “Expected” velocities of focus expansion were calculated from the time kernels, contact distributions, and gross reproductions. For both diseases, the observed and expected rates were in good agreement. A sensitivity analysis shows that the accuracy of the estimated variance of the contact distribution has a large influence on the accuracy of the predicted velocity. When the gross reproduction is small, the accuracy of its measurement also strongly contributes to the accuracy of the expected velocity of focus expansion.

Additional keywords: epidemiological models.