OZONE DAMAGE AND SEMIMATURE-TISSUE NEEDLE BLIGHT OF EASTERN WHITE PINE

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Abstract
Investigations were conducted in forests remote from large urban areas to determine whether there was any cause and effect relationship between naturally occurring atmospheric ozone (O3) and semimature-tissue needle blight (SNB) of eastern white pine (Pinus strobus). The daily average concentration of atmospheric ozone, relative to cracking by rubber test strips, was determined for three seasons and no apparent relationship was found between excessive rubber cracking and the occurrence of outbreaks of SNB on susceptible white pines. The repeated application of vitamin C, a reducing agent, to newly developing needles of susceptible white pines, did not prevent the appearance of the symptoms of SNB or retard subsequent symptom development. In fumigation experiments with artificially produced ozone, concentrations of over 0.60 p.p.m., as measured by the manual potassium iodide method, or 0.40 p.p.m. by the coulometric method, were required to produce severe markings on the new needles of the white pine under study. Foliage on material derived from trees non-susceptible to SNB was more responsive to these high concentrations of ozone and exhibited more uniform damage than foliage derived from trees susceptible to SNB. The macroscopic and microscopic symptoms of damage caused by excess ozone were dissimilar from the typical symptoms of SNB. The results of these investigations indicate that naturally occurring atmospheric ozone in stands of eastern white pine is not an incitant of SNB.
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