Does ozone negatively affect durum wheat?

Agricultural production is supposed to be negatively affected by ozone, particularly in the Mediterranean countries where the photochemical formation of this pollutant is high. However, the sensitivity of crops to the consequent oxidative stress largely depends on species and variety. In this work the ozone sensitivity of two cultivars of durum wheat (Neodur and Virgilio) was tested in an Open-Top Chambers experiment at Curno (Po Valley, Italy). A factorial design was used with two levels of ozone concentrations: charcoal filtered air (ambient air -50%) and ozone enriched air (+35%). A total number of 8 OTCs was used in order to have 4 replicates of the two ozone treatments. Seven pots of each cultivar were placed within each OTC and three durum wheat plants were grown in each pot, keeping the irrigation at field capacity. The experiment was carried on between February and the end of June in 2011. Onset and diffusion of leaf visible symptoms were measured with periodical visual assessments; flag-leaves samples were collected for microscopic and hystochemical analysis. Stomatal conductance to water was measured on flag-leaves at morning, midday and afternoon, in six different dates between 1st May and 15th June. Main agronomical yield parameters were evaluated after the harvesting (28th June). At the end of the growing season the ozone enriched plants experienced an AOT40 ozone exposure of 23’000 ppb·h vs an AOT40 of 700 ppb·h of the control plants. Although cv Virgilio shown considerable leaf injuries in the ozone enriched treatment, no significant effects on yield parameters were detected. The same result was obtained for cv Neodur which developed visible symptoms with a lower intensity and diffusion than Virgilio. Ozone reduced the number of empty earns (n.s.) and increased the dry weight of the stems (n.s.), while negligible differences on total grain weight in both cultivars were found. Plant’s gs response to ozone was contrasting in the two cultivars, being decreased in ozone treated Neodur and increased in the cv Virgilio with the same treatment. The opposite stomatal behavior could explain the different susceptibility of the two cultivars to ozone in relation to leaf injuries onset. Nevertheless the onset of leaf visible injuries and their diffusion could not be taken as a reliable predictor of yield losses at all. On the contrary, being the cv Virgilio more productive than the cv Neodur (+12% in the non-treated plants) the farmers should prefer Virgilio regardless of the foliar symptoms development. Compared to the bread wheat, the durum wheat resulted an ozone tolerant species. The blanket application of the critical levels based on dose-response relationships for bread wheat, hence, could be very penalizing for those Mediterranean countries, such as Italy, where 2/3 of the arable land used for wheat are assigned to the cultivation of durum wheat.