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The Relative Susceptibility of Eighteen Coniferous Species to Ozone. Donald D. Davis, Former Special Fellow, currently Air Pollution Specialist, U.S. Forest Service, State and Private Forestry, Division of Forest Pest Control, Asheville, North Carolina 28803, now Research Associate, Center for Air Environment Studies; Francis A. Wood, Professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 62:14-19. Accepted for publication 2 July 1971. DOI: 10.1094/Phyto-62-14.

Eighteen species of 2- to 6-year-old coniferous tree seedlings were exposed to 10 pphm O₃ for 8 hr or to 25 pphm O₃ for 4-8 hr. Virginia pine, jack pine, European larch, Austrian pine, Scotch pine, eastern white pine, eastern hemlock, Japanese larch, and pitch pine were susceptible. Arborvitae, balsam fir, Douglas fir, white fir, red pine, black hills spruce, Colorado blue spruce, Norway spruce, and white spruce were resistant to the highest dose. The incidence of sensitive plants within susceptible species populations ranged from 6-69%. Variable symptom response was observed among different species, among individual plants of the same species, and among different branches and needles of the same plant. Chlorotic mottle and tip necrosis or complete needle necrosis were the most commonly observed symptoms. Susceptible species were sensitive from the 4th through 13th weeks after budbreak. Seedlings in the dormant condition were resistant.