Natural and man-made selection for air pollution resistance

All manner of domestic and industrial activities lead to the injection of potentially toxic contaminants in to the air. Most have little or no discernible impact on the environment, because the resulting concentrations in the atmosphere fall well below the threshold for effects. Others attain levels that are known to exceed the recognized thresholds for damage to both fauna and flora. In this review the focus is on two of the most ubiquitous air pollutants-sulphur dioxide (SO2) and ozone (O-3). In many industrialized regions, ground-level concentrations of these gases are known to be high enough to depress crop yields and cause subtle shifts in the composition of natural (and semi-natural) plant communities. Consequently, these pollutants constitute a novel evolutionary challenge for natural and managed ecosystems. Herein, evidence is presented that some species are capable of responding to this challenge by evolving the ability to grow and reproduce in areas subjected to potentially phytotoxic pollutant concentrations. The prospects for breeding plants with enhanced resistance to the most common air pollutants are discussed and the tangible prospects of incorporating modern molecular approaches into existing strategies for the identification, isolation and manipulation of air pollution resistance in new stock are highlighted.