Factors influencing visible ozone injury on potato including the interaction with carbon dioxide

Weekly observations and scoring of ozone injury were done on all experimental sites where continuous monitoring of ozone in ambient air was available. Typical acute symptoms were reddish-brown lesions and bronzing, primarily on the upper surface of the leaves. The potato cultivar Bintje, cultivated at all sites, appeared to be sensitive to ozone but less than clover species, which served as model for the short-term critical level (AOT40/5 d). At the mid-European and Nordic latitudes injury appeared after an AOT40/5 d exposure of about 700 and 275 nl 1(-1) h, respectively. In central Europe the plants were indeed less sensitive than in Scandinavia and the AOT40/5 d values were higher than the proposed critical level of 500 nl 1(-1) h at a vapour pressure deficit (VPD) exceeding 1.5 kPa and 200 nl 1(-1) h at a VPD below 1.5 kPa. In addition injury appeared primarily after the stage of maximum leaf area (MLA). In the Nordic countries injury was noticed at very low AOT40/5 d values and occurred before as well as after the stage of MLA. Using artificial neural network models it appeared from the data set that VPD did not play a major role in the ozone sensitivity of potato, but there were indications that daylength was an important parameter in addition to a possible higher uptake at high latitudes. Increasing the CO2 concentration did not prevent the potato plants from visible ozone damage but it reduced the intensity by 10%. Taking only the OTC experiments of the mid-latitudes into account, there was a correlation between the ozone injury scoring just before harvest and the marketable yield loss. However, in all the cases considered, ozone damage appeared only after the stage of MLA and increased steadily towards harvest. The correlation can be explained by a parallel development of injury and chlorosis (senescence) typical for chronic exposure. There was no relationship between isolated short-term exposures causing acute injury and final yield. (C) 2002 Elsevier Science B.V. All rights reserved.