Differential Ozone Responses Identified among Key Rust-Susceptible Wheat Genotypes

Increasing ambient ozone (O-3) concentrations and resurgent rust diseases are two concomitant limiting factors to wheat production worldwide. Breeding resilient wheat cultivars bearing rust resistance and O-3 tolerance while maintaining high yield is critical for global food security. This study aims at identifying ozone tolerance among key rust-susceptible wheat genotypes [Rust near-universal susceptible genotypes (RnUS)], as a first step towards achieving this goal. Tested RnUS included seven bread wheat genotypes (Chinese Spring, Line E, Little Club, LMPG 6, McNair 701, Morocco and Thatcher), and one durum wheat line (Rusty). Plants were treated with five O-3 concentrations (CF, 50, 70, 90, and 110 ppb), in two O-3 exposure systems [continuous stirred tank reactors (CSTR) and outdoor-plant environment chambers (OPEC)], at 21-23 Zadoks decimal growth stage. Visible injury and biomass accumulation rate were used to assess O-3 responses. Visible injury data showed consistent order of genotype sensitivity (Thatcher, LMPG 6 > McNair 701, Rusty > Line E, Morocco, Little Club > Chinese Spring). Additionally, leaves at different orders showed differential O-3 responses. Biomass accumulation under O-3 stress showed similar results for the bread wheat genotypes. However, the durum wheat line Rusty had the most O-3-sensitive biomass production, providing a contrasting O-3 response to the tolerance reported in durum wheat. Chinese Spring was the most tolerant genotype based on both parameters and could be used as a source for O-3 tolerance, while sensitive genotypes could be used as sensitive parents in mapping O-3 tolerance in bread wheat. The suitability of visible symptoms and biomass responses in high-throughput screening of wheat for O-3 tolerance was discussed. The results presented in this research could assist in developing future approaches to accelerate breeding wheat for O-3 tolerance using existing breeding materials.