Flecking, plant injury

Ozone is generally recognized as the most important phytotoxicant in the oxidant complex. Early studies were reported in 1864. The phytotoxicity was firmly established in 1914, and this was confirmed in laboratory studies in 1937. It was first shown as a phytotoxic component (causing grape stipple) of the oxidant complex in 1958 and later as the cause of weather fleck of tobacco. Ozone is now known to cause injury to a multitude of broadleaved plants and to explain several types of needle injury in both eastern and western conifer species. 

In monocotyledonous plants (grasses and cereals) and some others, there is no division of mesophyll tissue, and injury normally appears as a bifacial fleck.Some plants, after extended exposure to low concentrations of pollution (either continuously or intermittently), produce chlorotic patterns that may be distinctive of oxidant pollution or similar to symptoms of normal senescence. The early senescence seen in some plants may be a result of long-term exposure to ambient oxidants. 

Brennan et using petunia, found a better correlation with atmospheric aldehydes than with total oxidants. This appears spurious, because researchers do not regard aldehydes themselves as important atmospheric phytotoxicants. Macdowall et were able to correlate tobacco injury with oxidant concentrations by considering ozone flux into plant leaves. They then predicted fleck attacks with fair consistency on the basis of meteorologic considerations. Several investigators have used acknowledged plant sensitivity and emphasized the importance of... 

Flecking on the upper surface of leaves is a common symptom of ozone injury on dicotyledonous plants. A single fleck is a small line of dead tissue that appears white, yellow, or brown... 

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