Enhancing physiological performance and quality traits of lettuce (Lactuca sativa L. cv. 'Batavia') through red–blue light ratio and γ-aminobutyric acid interplay

The integration of tailored light spectra and γ-aminobutyric acid (GABA) supplementation represents a promising strategy for improving crop yield in controlled environment agriculture (CEA). This study investigated the combined effects of Red (R):Blue (B) light ratios (RB: 90:10, 80:20, and 70:30) and 25 μmol L−1 GABA supplementation (G25) compared with the control (G0) on growth, chlorophyll fluorescence, and quality of Lactuca sativa L. cv. Batavia in a vertical farming system. Plant morphology was modulated by light spectrum and GABA. The RB:80:20 + G25 treatment significantly increased leaf anthocyanin content by 31.3%, leaf area by 15.4%, total fresh weight by 20%, and soluble carbohydrate content by 26.3% compared to the control plants. In contrast, the RB:70:30 treatment directed plant growth toward the roots. However, GABA application increased biomass reallocation toward the shoots by 60%. GABA application reduced the excess excitation energy (DI0/RC) by 11.76%, highlighting its role in improving light use efficiency. The highest Fj and F0 values were recorded in RB:90:10 + G25 and RB:80:20 + G25 treatments, respectively. This indicates the greater absorption range of R light by leaf chlorophylls, its impact on plant photosynthesis and the importance of GABA in modulating light transmission in the O-J phase. Sensory evaluation confirmed that RB:80:20 + G25 scored the highest for visual quality and taste. These findings suggest that precise combinations of R:B light ratios and GABA supplementation can simultaneously enhance and optimize both physiological performance and consumer-oriented quality traits in lettuce. Future research should investigate the molecular mechanisms underlying these interactions and their potential application to other leafy crops in CEA systems.