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Varietal Tolerance of Tobacco to Ozone Dose Rate

We determined the relative degree of ozone injury to genetically susceptible and resistant tobacco (Nicotiana tabacum L.) plants in studies of ozone tolerance. Essentially equal ozone doses derived from three ozone concentrations and nine exposure intervals were imposed on three tobacco varieties in fumigation experiments. Length of exposure determined relative injury at 0.10 ppm, but ozone concentration controlled injury when plants were exposed at 0.20 and 0.30 ppm. Ozone-resistant cv. ‘Bel-B’ sustained less than 10% total injury from a 0.15 ppmhr dose given at any of the three ozone concentrations. A 0.15 ppmhr dose, however, caused significantly greater injury to ozone-susceptible cv. ‘Bel-W3’ at the two higher ozone concentrations. Ozone caused almost 40% leaf injury to Bel-B when we exposed plants to a 0.30 ppmhr dose at 0.20 and 0.30 ppm, but total injury remained near 10% when the 0.30 ppmhr dose was given at 0.10 ppm. Results indicate that varietal response to ozone is controlled by exposure interval and concentration rather than ozone concentration independently. Ozone dose rate affected the size of fleck lesions displayed by Bel-W3. Leaves exposed for 6 hr at 0.10 ppm developed flecks four to six times larger than the flecks obtained after 1 hour at 0.30 ppm.

Key Words: ozone fleck • stomatal impressions

Received for publication December 21, 1967.