• Higher B-type LMW-GS expression in modern genotypes contributes to gluten strength. • A marked decrease in ω-type gliadin expression is observed in modern genotypes. • Differences in ω-5 gliadin expression appear also related to the number of isoforms. • Old and modern genotypes show similar α- and γ-type gliadin expression. • A higher ω-gliadins and HMW-GS content was observed under water deficit.

Due to climate change, the application of water saving strategies is of particular interest. The aim of this study was to evaluate the effects of deficit irrigation (DI) and partial root-zone drying (PRD) techniques on the crop water stress index (CWSI), water use efficiency (WUE), and quality parameters in processing tomatoes grown in open field conditions in a Mediterranean climate. Two cultivars were grown for two growing seasons under four irrigation regimes as follows: (i) IR₁₀₀: full irrigation by restoring 100% of the maximum tomato evapotranspiration (ET_c); (ii) IR_70DI: 70% of the amount of water given to the IR₁₀₀; (iii) IR_70PRD: 70% of the amount of water given to the IR₁₀₀ by applying partial root-zone drying and (iv) IR₀: irrigation only at transplanting and during fertigation. During the flowering period, the first growing season was characterized by an absence of rainfall and by higher temperatures also showing a higher CWSI. Despite, under IR_70PRD, the CWSI was significantly higher than under IR_70DI, the marketable yield obtained was significantly higher. Both IR_70DI and IR_70PRD regimes received approximately 24% less water than IR₁₀₀, but the yield reduction with relation to the optimum regime was equal to 16.2% under IR_70DI, and only 7.6% under IR_70PRD. The WUE increment of IR_70PRD with respect to IR₁₀₀ was equal to 27% in the first growing season and to 17% in the second one, showing that the positive effect of PRD on the WUE is more evident in the more stressed year. Finally, the results from the principal component analysis (PCA) showed that the two cultivars had different qualitative responses in the two extreme regimes (IR₁₀₀ and IR₀) but not under PRD and DI regimes.