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Effect of Ozone on the Wheat Stem Rust Fungus. Allen S. Heagle, Plant Pathologist, Plant Science Research Division, ARS, USDA, Department of Plant Pathology, North Carolina State University, Raleigh 27607; Linda W. Key, Microbiologist, Division of Ecological Research, Environmental Protection Agency, National Environmental Research Center, Research Triangle Park, North Carolina 27711. Phytopathology 63:397-400. Accepted for publication 3 October 1972. DOI: 10.1094/Phyto-63-397.

The effects of low concentrations of ozone on various phases of the uredial cycle of the wheat stem rust fungus were studied. Daily 6-hr ozone exposures of infected plants significantly decreased the growth of hyphae and the number of urediospores produced. The mean spore production over a 17-day period was 90, 82, and 50% of the controls when plants were exposed for 6 hr/day for 17 days to 6, 12, and 18 pphm ozone, respectively. Ozone exposures 24 to 48 hr before inoculation injured the plants and reduced penetration and infection. When plants were inoculated immediately after exposure and before injury developed, no reduction in penetration and infection occurred. Germination and infection of wheat plants by spores produced on exposed plants was not affected when these spores were used to inoculate plants not previously exposed.