Effects of Increasing Ozone Levels on Leaf Biochemistry and Flower Development in Petunia Varieties with Different Floral Pigmentation

In this work, we assessed the effects of increasing ozone (O3) on four petunia varieties with different floral pigmentation (pink, red, rose-red, and white). Plants were exposed, in open-top chambers located in China, to three O3 concentrations, i.e., (i) ambient air (AA), (ii) AA + 60 ppb O3 (AA + 60), and (iii) AA + 120 ppb O3 (AA + 120), for 85 days (9 h day−1). Flower diameter and duration were assessed, together with leaf chlorophyll and flavonoid contents. White petunia showed a reduced flower diameter and longevity under AA + 60 (−7 and −6%, respectively, in comparison to AA), whereas pink and red petunias only showed this under AA + 120 (−8 and −7%, on average, respectively). Chlorophyll loss occurred in all varieties under AA + 60 (−30%, on average), and at AA + 120 in white and red petunias (−54%, on average). The total flavonoid content in the pink and white varieties increased only under AA + 120 (around +85%), while it grew at both AA + 60 and AA + 120 (+92% and two-fold higher, respectively) in the red variety. Increasing O3 concentrations did not affect particularly the red-rose variety. The white variety showed the strongest correlations among flower and leaf properties, confirming a variety-related O3 response, as well as demonstrating that it had the highest O3 sensitivity.