VIEW ARTICLE

Ecology and Epidemiology

A Quantitative Model for Describing the Sporulation of Plasmopara viticola on Grape Leaves. N. Lalancette, Postdoctoral research associate, Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691; L. V. Madden, and M. A. Ellis. Associate professors, Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. Phytopathology 78:1316-1321. Accepted for publication 2 May 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-1316.

Leaves from potted grape vines of Vitis lambrusca ‘Catawba’ infected with downy mildew were placed in a dark moist chamber maintained at constant temperatures of 10, 15, 20, 25, and 30 C. A humidifier, located within the chamber, maintained atmospheric moisture at or near saturation. Plants were removed for observation after 6, 7.5, 9, 10.5, and 12 hr. The largest number of spores, approximately 300,000 sporangia per square centimeter of lesion area, were produced after 12 hr at 20 C, while no sporulation was observed at any time at 10 or 30 C. When the asymptote, rate, and intercept parameters of the Richards model were represented as quadratic functions of temperature, the model fitted to the pooled data described 90% of the variation in number of sporangia. The model predicted that approximately 50% of the sporangia were formed at 20 C after 8 hr of incubation. Although sporangia were produced after only 7.5 hr of incubation, they failed to germinate, possibly indicating a lack of maturity. However, germination increased as the duration of the sporulation period was increased, until a maximum of 70% was observed for sporangia harvested after 12 hr at 25 C.