Effects of Air Pollutants on Burley Tobacco Cultivars

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Abstract
Nine burley tobacco (Nicotiana tabacum L.) varieties were tested for susceptibility to air pollutants in fumigation chamber and field experiments. Ozone administered for short intervals (1.0 and 1.5 hours) at relatively high concentrations (30.0 and 20.0 pphm, respectively) caused significantly more leaf injury than when used for a longer period (3.0 hours) at a lower concentration (10.0 pphm). These tendencies were apparent even though total ozone dosages were about equal. At the lowest rate, ozone caused the most injury to ‘Burley 2’ and ‘Ky 16,’ and the least injury to ‘Burley 49’ and ‘Ky 9.’ Cultivars exhibited much smaller differences in degree of leaf injury when ozone was given at high as compared to low concentrations. Burley 2 and Ky 9 continued to be susceptible and tolerant, respectively, at the high rates. Response of the nine varieties to low concentration mixtures of ozone and sulfur dioxide revealed: (1) the two gases acted synergistically to cause injury; and (2) Burley 21 and Burley 49 reversed positions of susceptibility to mixed gases as compared to injury by ozone.In the field weather fleck was more severe on Burley 2, Burley 21, Ky 9 and Ky 16 than on ‘Burley llB’ and ‘Burley 37.’ The varieties that showed the greatest fleck tolerance were Burley 49 and ‘Ky 12.’ Ozone, the primary cause of weather fleck, reached a phytotoxic level of 5.0 pphm (Mast 724‐1) on 20 dates during July. Highest concentration recorded was 12.0 pphm on July 24.All varieties exposed to pollutants in the chamber displayed identical symptoms. Ozone at low dosages caused tiny, bleached stipples or flecks to appear on the upper leaf surface. Ozone and sulfur dioxide mixtures induced upper surface fleck‐like markings very similar to (but a little larger than) ozone lesions. Field symptoms of weather fleck consisted of characteristic ozone flecking on Burley 2, Burley 11B, Ky 9, Ky 12, and Ky 16 and biracial necrotic lesions (2.0 to 3.0 mm) on Burley 37, Burley 49, and ‘Ky 35.’

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