Ozone/biotic disease interactions: molecular biomarkers as a new experimental tool

Current climate change scenarios predict a further increase of tropospheric ozone which is well known to inhibit plant photosynthesis and growth processes. Ozone can also predispose plants to enhanced biotic attack, as proposed in particular for necrotrophic fungi, root-rot fungi and bark beetles. However, at present it does not seem possible to predict whether increased ambient ozone will lead to a higher or lower disease likelihood in particular plant-pathogen systems. It has been stated repeatedly in the literature that periods of high ambient ozone are essentially non-coincident with infection periods of most fungal pathogens. This implies minimal interactive risks. However, it now appears that the various ozone-induced metabolic changes can persist in plants over days or months. Visible ozone symptoms also may be greatly delayed. Certain stress transcripts, proteins and metabolites have been developed as ozone biomarkers in controlled exposure experiments, but these biomarkers remain to be examined on field sites. A simple epidemiological scenario based on 'memory' time spans of ozone effects is proposed as a tool to make ozone-plant disease interactions more predictable.