VIEW ARTICLE

Ecology and Epidemiology

Development of an Infection Efficiency Model for Plasmopara viticola on American Grape Based on Temperature and Duration of Leaf Wetness. N. Lalancette, Postdoctoral research associate, Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691; M. A. Ellis, and L. V. Madden. Associate professors, Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. Phytopathology 78:794-800. Accepted for publication 7 January 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-794.

The infection efficiency of Plasmopara viticola was determined for the American grape, Vitis lambrusca ‘Catawba.’ Leaves on potted vines were inoculated with the fungus and exposed to a range of wetness durations (1–15 hr) at each of six fixed temperatures (5–30 C) in a growth chamber. The Richards function was then used for describing the results. The maximum infection efficiency obtained at each temperature, a measure of the asymptote parameter of the Richards model, was derived as a function of temperature using a second-order polynomial; the models fit to the pooled and averaged data described 84 and 96%, respectively, of the variation in this parameter. An optimum maximum efficiency of 0.07–0.08 occurred at 15–20 C, whereas little or no disease occurred at the 5 and 30 C extremes. Similarly, the rate parameter of the Richards model also could be expressed as a quadratic function of temperature; the models fit to the pooled and averaged data explained 72 and 82%, respectively, of the variation in the rate. Values of this parameter ranged from 0 at 3.8 and 30 C to 0.36 at 16.9 C. After substituting the polynomials for the asymptote and rate parameters in the linearized version of the Richards function, the model described 73% (pooled data) and 84% (averaged data) of the variation in infection efficiency. At 15 and 20 C, the efficiency rapidly increased from approximately 0 after 2 hr wetness to 0.06 after 4–5 hr; subsequent increase was gradual until a maximum of 0.08 was reached at 15 hr and 15 C. At 10 and 25 C, the initial increase required approximately 8–10 hr of wetness before leveling off at an efficiency of 0.05–0.06.