The Leaf Roll-Necrosis Disorder of Lilacs: Etiological Role of Urban-Generated Air Pollutants1

Abstract

The leaf roll-necrosis disorder has been identified in collections of lilac (Syringa vulgaris L.) in or near the cities of New York, Philadelphia, and Boston. Observed symptom differences among lilacs at 6 sites were largely quantitative, indicating the occurrence of incitants common to all locations. Activated charcoal and 4,4’-dioctyldiphenylamine filter chambers applied to branches reduced injury and provided corroborating evidence that air pollutants, including oxidant-type, were causal factors. Monitoring data from New York City and Philadelphia revealed progressively decreasing pollutant levels in recent years that coincided with decreases in severity of the disorder. Fluoride was not a causal agent, based on low levels in leaves. In experimental fumigations of lilac clones, although the results were inconclusive regarding identification of causal pollutants, ozone and sulfur dioxide induced some symptoms of the disorder. The occurrence of additional field symptoms suggested the involvement of other, as yet unidentified, phytotoxic pollutants.