Estimating Infection Efficiency of Plasmopara viticola on Grape

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Abstract
To estimate the infection efficiency of Plasmopara viticola, the number of sporangia applied to a leaf and the number of zoospores they produced were determined. A relationship was developed between leaf area and the volume of inoculum retained without runoff. Given this relationship and the concentration of sporangia, the number of sporangia applied to a leaf could be estimated. Zoospore production from sporangial suspensions was examined in vitro at various temperatures; an average of seven zoospores per sporangium was observed over for incubation temperatures of 5-25 C. Finally, potted vines of Vitis labrusca cv. Catawba were inoculated with sporangial suspensions of different concentrations. Although disease severity increased with inoculum concentration, the infection efficiency was estimated to be about 6% for each treatment.

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