Ozone treatments to induce systemic-acquired resistance in leaves of potted vines: molecular responses and NIR evaluation for identifying effective dose and exposition duration

The European Community has recently imposed considerable restrictions on the use of pesticides, with the establishment of a regulatory framework for the sustainable use of agro-chemicals. However, in the viticulture sector, the intensive use of chemical pesticides, as well as sulfur and copper, is often required. Recently, ozone has been proposed as a possible environmentally friendly tool for controlling the development of pests on vines. However, little is known about the parameters linked to the practical application of ozone for controlling grapevine pests and how it triggers plant defence mechanisms. The main aim of this preliminary study was to determine the concentration of ozone and exposure duration in a treatment for stimulating the expression of systemic acquired resistance (SAR)-related genes, without inducing toxic effects and affecting vine health. In the first trial, three different combinations of ozone concentration and duration of treatment were tested on potted grapevines: i) gaseous ozone at 300 ppb for 12 hours, ii) gaseous ozone at 100 ppb for 6 hours, and iii) gaseous ozone at 100 ppb for 3 hours. Based on the results of the first trial, the potted vines were treated with just 100 ppb for 3 hours in a second trial. Leaves at different developmental stages were sampled. The expression level of systemic acquired resistance-related genes was analysed 12 hours and 7 days after each treatment. Furthermore, physiological parameters and NIR spectra were analysed. Ozone induced a transient up-regulation (limited to 12 hours after the treatments) of chitinases, beta-1,3-glucanase and glutathione-S-transferase. On the other hand, pathogen-related (PR) genes showed a more persistent over-expression. The ozone treatment selectively affected the stomatal conductance depending on the different ozone concentrations. Detected NIR spectra revealed significant structural changes in ozone-treated plants, especially in leaves exposed to higher concentrations of ozone. These results suggest that ozone is able to transiently stimulate the expression of some resistance-related genes even at low and non-toxic doses for the vine leaves.