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Germination of Phyllosticta maydis Conidia in An Incubation Chamber with Control of High Relative Humidities. A. Bootsma, Former graduate student, Department of Land Resource Science, University of Guelph, Guelph, Ontario, Present address of senior author: Department of Agriculture and Forestry, Charlottetown, Prince Edward Island; T. J. Gillespie(2), and J. C. Sutton(3). (2)Assistant Professor, Department of Land Resource Science, University of Guelph, Guelph, Ontario; (3)Assistant Professor, Department of Environmental Biology, University of Guelph, Guelph, Ontario. Phytopathology 63:1157-1161. Accepted for publication 6 March 1973. DOI: 10.1094/Phyto-63-1157.

Control of relative humidity (RH) to within ± 0.6% was achieved in the range from 94% to saturation, in a 1-liter chamber maintained in the dark and at 20 C for 3 days by means of two continuous air streams saturated with water vapor at different temperatures. An accuracy of ± 0.15% at 98% RH was obtained over 5-10 hours. The system was designed to incubate conidia of Phyllosticta maydis on detached maize leaf segments or glass slides, but is adaptable for studying various host-parasite combinations on attached leaves or entire plants. Germination of P. maydis conidia on glass slides was similar to that on maize leaf segments and percent germination decreased from a maximum at 100% RH to zero at 94% RH.