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The Influence of Environmental Factors on the Sensitivity of Virginia Pine to Ozone. Donald D. Davis, Former Special Fellow, currently Assistant Professor and Extension Air Pollution Specialist, Department of Plant Pathology and Center for Air Environment Studies, The Pennsylvania State University, University Park 16802; Francis A. Wood, Research Associate, Center for Air Environment Studies, and Professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 63:371-376. Accepted for publication 9 September 1972. DOI: 10.1094/Phyto-63-371.

Virginia pine seedlings were injured more severely when exposed to 25 pphm O₃ for 4 hr at high humidities than when exposed to this dose at low humidities. The percent relative humidity at which plants were maintained before or after exposure did not affect the amount of injury. An inverse relationship was observed between exposure temperature and degree of plant injury. In contrast, a direct correlation was observed between the temperature at which plants were maintained before and after exposure and the amount of O₃ injury. Seedlings kept in the light for 24 hr or longer prior to exposure were protected from injury. Plants maintained in darkness for periods up to 96 hr before exposure were injured. Postexposure extended light periods did not affect symptom development; however, extended dark periods following exposure delayed typical symptom development until the seedlings were placed in the light.