Enhancing Plant Protection Against Ozone-Induced Toxic Stress: An Unexplored Application of Grafting in Phaseolus vulgaris L.

Tropospheric ozone (O 3 ) is an air pollutant and phytotoxic stressor that impairs plant physiology and causes chlorotic and necrotic lesions on leaves. While shoot responses are well characterized, the role of root in plant tolerance to O 3 is not elucidated yet. Here, the O 3 -sensitive Pinto common bean cultivar (PI) was reciprocally grafted onto a common bean O 3 -tolerant genotype (R) or the Greek landrace Zargana Kavalas, (ZK) to investigate rootstock effects on plant O 3 responses. Self-grafted (PI/PI, R/R, ZK/ZK), non-grafted (PI, R, ZK), and hetero-grafted (PI/R, PI/ZK, R/PI, ZK/PI) plants were grown in separate walk-in chambers and subjected to either charcoal-filtered air (CF-air) or O 3 -enriched air (eO 3 ; 150 ppb × 7 days × 8 h day −1 ). Under eO 3 treatment, both self-grafted and non-grafted PI plants exhibited ~ 33% visible injury, decreased photosynthetic assimilation rate ( A ), stomatal conductance (g s ), and CO 2 use efficiency (CUE), reduced photosynthetic pigment content, and elevated oxidative stress indicators (malondialdehyde content, proline, total phenolics, chlorophyll fluorescence). In contrast, grafted sensitive plants onto tolerant rootstocks showed limited visible injuries (< 2%) and maintained more stable physiological and biochemical traits. These findings suggest that plant sensitivity/tolerance to O 3 is root-mediated, and support grafting as a promising strategy to improve plant tolerance to O 3 stress.