Understanding and improving global crop response to ozone pollution

Concentrations of ground-level ozone ([O-3]) over much of the Earth's land surface have more than doubled since pre-industrial times. The air pollutant is highly variable over time and space, which makes it difficult to assess the average agronomic and economic impacts of the pollutant as well as to breed crops for O-3 tolerance. Recent modeling efforts have improved quantitative understanding of the effects of current and future [O-3] on global crop productivity, and experimental advances have improved understanding of the cellular O-3 sensing, signaling and response mechanisms. This work provides the fundamental background and justification for breeding and biotechnological approaches for improving O-3 tolerance in crops. There is considerable within-species variation in O-3 tolerance in crops, which has been used to create mapping populations for screening. Quantitative trait loci (QTL) for O-3 tolerance have been identified in model and crop species, and although none has been cloned to date, transcript profiling experiments have identified candidate genes associated with QTL. Biotechnological strategies for improving O-3 tolerance are also being tested, although there is considerable research to be done before O-3-tolerant germplasm is available to growers for most crops. Strategies to improve O-3 tolerance in crops have been hampered by the lack of translation of laboratory experiments to the field, and the lack of correlation between visual leaf-level O-3 damage and yield loss to O-3 stress. Future efforts to screen mapping populations in the field and to identify more promising phenotypes for O-3 tolerance are needed.