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Disease Detection and Losses

Effects of Daily Ozone Exposure Duration and Concentration Fluctuation on Yield of Tobacco. Allen S. Heagle, Plant pathologist, USDA-ARS, Department of Plant Pathology, North Carolina State University, Raleigh 27650; W. W. Heck(2), V. M. Lesser(3), and J. O. Rawlings(4). (2)Plant physiologist, USDA-ARS, Department of Botany, North Carolina State University, Raleigh 27650; (3)Statistician, Department of Statistics, North Carolina State University, Raleigh 27650; (4)Professor of statistics, Department of Statistics, North Carolina State University, Raleigh 27650. Phytopathology 77:856-862. Accepted for publication 3 December 1986. 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, 1987. DOI: 10.1094/Phyto-77-856.

Flue-cured tobacco (Nicotiana tabacum ‘McNair 944’) was exposed to chronic doses of ozone (O₃) in open-top field chambers to determine the influence of frequency and magnitude of peak O₃ concentrations and daily exposure duration on tobacco yield response. The treatments were established by adding O₃ in amounts that were proportional to ambient O₃ concentrations or in constant amounts. The frequency of occurrence and level of peak O₃ concentrations were greater for each proportional-addition treatment than for the corresponding constant-addition treatments. However, the seasonal mean O₃ concentrations were nearly identical, and the yield response to O₃ was similar for both types of O₃ addition. Yield in plots receiving proportional addition of O₃ for 12 hr/day (1000 to 2200 hours EDT) was 10% less (three treatment levels combined) than in those receiving proportional addition for 7 hr/day (1000 to 1700 hours EDT). If other important crop species have a similar response to O₃ late in the afternoon, previous national crop loss estimates based on seasonal 7-hr/day O₃ exposures may be low.