Morphological changes in two tobacco and petunia cultivars under exposure to tropospheric ozone

The study assessed the effect of cumulative tropospheric ozone on the morphology of an ozone-sensitive (Bel W3) and an ozone-resistant (Bel B) tobacco cultivar, and two petunia cultivars (Mirage, White Cascade). The plants were exposed at two sites differing in tropospheric ozone level for two months during the 2008 growing season. Similar sets of plants were cultivated in control conditions. Morphological parameters of the plants were measured every week during the experiment. The correlation between the recorded results and the cumulative concentrations of tropospheric ozone measured at the two exposure sites was estimated. The ozone-sensitive tobacco cultivar showed increased visible damage after four weeks of the experiment, although ozone was relatively low during the preceding weeks, possibly confirming the cumulative effect of ozone on the plant response. The ozone-resistant tobacco cultivar showed higher mean plant growth and leaf growth than the ozone-sensitive one throughout the experimental period, but at the exposure sites the ozone-sensitive cultivar showed plant growth similar to or higher than the controls, especially at the forest site where ozone concentrations were higher. This suggests a plant defense against reduction of leaf assimilation area (i.e., against leaf necrosis). Petunia cv. Mirage showed lower growth at the control site and had fewer flowers than White Cascade at all sites. White Cascade had more flowers than Mirage in the last week of the experiment at the forest site where tropospheric ozone was higher. Its mean growth was higher at the forest site than at the other exposure site