Ozone Effects on Seedlings of Rocky Mountain Ponderosa Pine. William M. Aitken, Graduate Research Assistant, Department of Botany and Plant Pathology, Colorado State University. W. R. Jacobi, Assistant Professor, Department of Botany and Plant Pathology, Colorado State University, and J. M. Staley, Former Research Plant Pathologist, USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins 80523. Plant Dis. 68:398-401. Accepted for publication 24 November 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-398.

Two-year-old seedlings of Rocky Mountain ponderosa pine (Pinus ponderosa var. scopulorum) were fumigated in greenhouse chambers at 0.50 (980 μg/m³), 0.40 (784 μg/m³), 0.30 (588 μg/m³), or 0.25 (490 μg/m³) ppm from 0800 to 1800 hours for 21 days. Seedlings fumigated at 0.50, 0.40, and 0.30 ppm showed mottling and chlorosis of needles. No visual symptoms were observed on seedlings fumigated at 0.25 ppm. Compared with untreated controls, 4-yr-old seedlings fumigated at 0.50 ppm ozone from 0900 to 1800 hours for 18 days had significantly depleted chlorophyll contents in each of four age classes of needles.