VIEW ARTICLE

Ecology and Epidemiology

A Model Relating the Probability of Foliar Disease Incidence to the Population Frequencies of Bacterial Plant Pathogens. D. I. Rouse, Department of Plant Pathology, University of Wisconsin, Madison 53706; E. V. Nordheim(2), S. S. Hirano(3), and C. D. Upper(4). (2)Statistics/Forestry, University of Wisconsin, Madison 53706; (3)Department of Plant Pathology, University of Wisconsin, Madison 53706; (4)Department of Plant Pathology, also Agricultural Research Service, USDA, University of Wisconsin, Madison 53706. Phytopathology 75:505-509. Accepted for publication 30 October 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-505.

A model has been developed that relates pathogen population size on individual leaves at time t₀ to disease incidence at some later time t₁. The lognormal distribution is used to describe population size of pathogenic bacteria on individual leaves, and the probit function is used to describe the probability of disease, given a bacterial population size. When integrated with respect to bacterial population frequency, the product of the probability of disease, given a bacterial population size, for individual leaves and the frequency of pathogenic bacteria on individual leaves results in a cumulative normal frequency distribution. This distribution function describes the probability of disease incidence (as frequency of diseased leaflets) in a field. To illustrate its use, the model was applied to bacterial brown spot of beans caused by Pseudomonas syringae pv. syringae. A maximum-likelihood technique was used to estimate the mean and variance of bacterial population size from censored samples.