Effects of Air Pollution on Maryland (Type 32) Tobacco

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Abstract
Six Maryland tobacco (Nicotiana tabacum L.) cultivars were tested for resistance to air pollutants. Fumigation chamber tests disclosed that ozone used at 5 pphm for 6 hours destroyed about 10% of the leaves of ‘Catterton’, and injured 5 to 8% of the leaves of other cultivars. Ozone administered for three hours at 15 pphm damaged about one‐third of the leaves and injured about two‐thirds of the leaf surfaces when the concentration was increased to 30 pphm. When plants were exposed to 22 pphm for 3 hours, injury was 2 to 8% greater than was observed at 15 pphm. ‘Wilson’ was more resistant to ozone than ‘Maryland 10’, ‘Maryland 59’, ‘Maryland 64’, ‘Maryland 609’, and Catterton. Maryland 10 and Maryland 59 tended to be as ozone‐susceptible as Catterton. Maryland 64 and Maryland 609 resembled the ozone response of Wilson. None of the differences in susceptibility were statistically significant except between Catterton and Wilson.Ozone and sulfur dioxide mixtures acted synergistically to inflict ozone‐type symptoms on all Maryland cultivars. No injury resulted when plants were fumigated singly for 4 hours with ozone at 3 to 3.5 pphm and sulfur dioxide at 45 to 50 pphm. The combination of these gases at the same concentrations and time interval produced 5 to 15% leaf injury. Twice as much injury occurred when mixed gases were used for 2 hours at 10 to 12 pphm ozone and 45 to 50 pphm sulfur dioxide. Sulfur dioxide injury thresholds were barely reached by a 3‐hour exposure at 150 pphm. Estimated injury ranged from 2 to 6%.Stomatal characteristics of the six cultivars varied within a 3 cm2 area of a leaf at prime ozone susceptibility. Stomatal frequency may have been a more important factor controlling ozone injury than the diameter of apertures. Catterton and Maryland 10 showed almost 10 stomata/field compared to 6 stomata/field on leaves of Wilson.Field studies in the five‐county Southern Maryland District disclosed a general correlation between resistance to ozone and resistance to weather fleck. Wilson, Maryland 64, and Maryland 609 were more fleck tolerant than Maryland 10, Maryland 59, and Catterton. Fleck was more severe in counties that were adjacent to Washington, D. C., and Baltimore, Maryland. Extensive fleck damage occurred, however, at a location 42 miles south/southeast of the District of Columbia. The severity of symptoms on Maryland cultivars and on such fleck‐susceptible cultivars as ‘BeI‐W3’, ‘Burley 21’, and ‘Havana 142’ suggested that during periods of air stagnation, oxidants probably exceed 10 pphm (Mast) throughout most of the Type 32 area, and are responsible for most of the fleck damage.

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