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An Apparatus for Accurate Control of Atmospheric Water Potentials in Studies of Foliar Plant Pathogens. H. Hartmann, Former graduate student, Department of Environmental Biology, University of Guelph, Guelph, Ontario, N1G 2W1, Present address of the senior author: Agriculture Canada, Research Station, Sidney, British Columbia V8L 1M3, Canada; J. C. Sutton(2), and G. W. Thurtell(3). (2)Associate professor, Department of Environmental Biology, University of Guelph, Guelph, Ontario, N1G 2W1; (3)Professor, Department of Land Resource Science, University of Guelph, Guelph, Ontario, N1G 2W1. Phytopathology 72:914-916. Accepted for publication 12 November 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-914.

An apparatus for precise and accurate control ( 10 bars) of atmospheric water potentials (φ) is described. Atmospheric φ of ≤1,000 to 0 bars at temperatures in the range of 1050 C can be produced and maintained in the apparatus for up to 5 days. Atmospheric φ may be changed and equilibrated at a different level within 1015 min. In the apparatus, Peronospora parasitica sporulated on infected cabbage seedlings only when atmospheric φ was > 60 bars. The apparatus is suitable for studies of atmospheric φ in relation to various stages of the infection cycles of foliar pathogens.

Additional keywords: Brassica oleracea var. capitata, downy mildew, relative humidity.