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Etiology

Thresholds for Injury, Growth, and Yield Loss Caused by Ozone on Field Corn Hybrids. A. S. Heagle, Plant pathologist, Southern Region, Science and Education Administration, US Department of Agriculture, Plant Pathology Department, North Carolina State University, Raleigh 27650; R. B. Philbeck(2), W. M. Knott(3). (2)Agricultural engineer, Southern Region, Science and Education Administration, US Department of Agriculture, Plant Pathology Department, North Carolina State University, Raleigh 27650; (3)Research associate, Botany Department, North Carolina State University. Phytopathology 69:21-26. Accepted for publication 24 July 1978. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1979. DOI: 10.1094/Phyto-69-21.

A commercial field corn (Zea mays L.) hybrid ‘Coker 16’ was exposed to four chronic doses of ozone (O₃) in open-top field chambers from 25 days after planting until maturity. The different doses were obtained by adding different but constant concentrations of O₃ to the naturally varying ambient concentrations for 7 hr/day (from 0930 to 1630 hours). The threshold O₃ concentrations causing foliar injury (between 0.02 and 0.07 ppm) were lower than concentrations required to decrease kernel yield (between 0.11 and 0.15 ppm). These thresholds were the same whether plants were grown in pots or in the ground. In the greenhouse, the sensitivity of Coker 16 to growth effects caused by chronic O₃ exposures was intermediate to that of two open-pedigree hybrids. In the field, both open-pedigree hybrids were more sensitive than Coker 16. Exposure to a mean O₃ concentration of 0.15 ppm for 7 hr/day decreased kernel yield of the open-pedigree hybrids by 37–40%, but that of Coker 16 was decreased by only 12%.