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Ecology and Epidemiology

Infection Rates in Three Pathosystem Epidemics Initiated With Reduced Disease Severities. J. L. Plaut, Former graduate student, Dept. of Plant Pathology, University of Florida, Gainesville 32611; R. D. Berger, professor, Dept. of Plant Pathology, University of Florida, Gainesville 32611. Phytopathology 71:917-921. Accepted for publication 9 January 1981. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-917.

The progress of bean rust (caused by Uromyces phaseoli), early leafspot (caused by Cercospora arachidicola) of peanut, and grey blight (caused by Botrytis cinerea) of begonia was monitored in epidemics initiated with high, medium, and low levels of inoculum. Polycyclic grey blight and bean rust epidemics developed in replicated greenhouse chambers equipped to simulate field weather conditions and bean rust and early leafspot epidemics were studied in buffered field plots. The Gompertz transformation of the disease proportions consistently provided a better statistical fit than did the logistic transformation when both were tested by simple linear regression. Polynomial models were inferior to the simple linear regression models. When the disease proportions were transformed with the logistic equation, rapid, nonlinear disease increases aberrantly were projected for initial epidemic stages. Regardless of the transformation, model, pathosystem, or experimental location, the calculated rates of disease increase were greatest for epidemics starting from the lowest initial disease severity in 73% of all cases. Low initial disease apparently was compensated for by accelerated rates of disease increase. Thus, sanitation measures in the management of compound interest diseases may be less effective than previously theorized.