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Coupling a Disease Progress Model for Early Blight to a Model of Potato Growth. K. B. Johnson, Former research associate/lecturer, Department of Plant Pathology, University of Minnesota, St. Paul 55108, Present address: Dept. of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902; P. S. Teng, former professor, Department of Plant Pathology, University of Minnesota, St. Paul 55108, Present address: Dept. of Plant Pathology, International Rice Research Institute, Los Banos, The Philippines. Phytopathology 80:416-425. Accepted for publication 15 October 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-416.

A disease progress model for early blight disease, caused by Alternaria solani, was coupled to a dynamic potato growth model that accumulates and partitions dry matter into leaves, stems, roots, and tubers. The disease progress model was a modified logistic with terms for new infection, lesion expansion, and a variable incubation period. In the crop model, new infection and lesion expansion reduced green leaf tissue, and cohorts of leaf tissue were prematurely senesced after a maximum proportional lesion severity was attained. In field experiments, incubation period was found to depend on the age of leaf tissue, and the proportional lesion area that induced leaf senescence was dependent on the age of the crop. Observed relative lesion expansion rates (day) were independent of leaf or crop age. Values for the infection rate parameter were determined by fitting the model to periodically sampled crop biomass and disease severity data from inoculated field plots of Russet Burbank potato. Compared to controls, both observed and simulated epidemics did not reduce tuber yield until late in the season. In simulation analyses, reductions in tuber yield were most sensitive to changes in the rate of lesion expansion followed by the time of disease onset. When early blight epidemics were initiated early in the season, the incubation period and the rate of leaf area expansion limited the rate of disease progress until near midseason. Simulated epidemics with onset times in the last quarter of the season had little effect on tuber yield.

Additional keywords: epidemiology, pest management, simulation modeling, Solanum tuberosum, yield loss.