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Effects of Ozone and Sulfur Dioxide on the Host-Pathogen Relationship of Scotch Pine and Scirrhia acicola. T. C. Weidensaul, Professor of plant pathology and forestry, Ohio Agricultural Research and Development Center, College of Wooster, Wooster, OH 44691; S. L. Darling, senior, College of Wooster, Wooster, OH 44691. Phytopathology 69:939-941. Accepted for publication 7 March 1979. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Association of Cereal Chemists, Inc., 1979. DOI: 10.1094/Phyto-69-939.

Scotch pine seedlings from five seed sources were inoculated with Scirrhia acicola 5 days before or 30 min after fumigation for 6 hr with 533 μg/m3 (0.20 ppm) of sulfur dioxide, 399 μg/m3 (0.20 ppm) of ozone, or the same levels of ozone and sulfur dioxide combined. After 8 wk, seedlings inoculated 5 days before fumigation had more lesions incited by S. acicola than those inoculated 30 min after fumigation. Ozone caused more needle injury than sulfur dioxide did. The amount of injury caused by the combined gases was a greater-than-additive effect. The degree of infection varied significantly among the seed sources.