How does the light spectrum affect bioactive compounds in green and purple basils grown hydroponically in a vertical farming system?

The light spectrum plays a fundamental role in modulating plant growth and the biosynthesis of bioactive compounds in crops such as basil ( Ocimum basilicum L.). This study evaluated the influence of different LED light spectra on the agronomic and functional parameters of two basil cultivars (green and purple) grown in a vertical hydroponic system. Four spectral treatments with varying Red:Blue (R:B) ratios were tested: 1:1, 2:1, 3:1, and 5:1, maintained at a constant light intensity of 250 µmol m⁻² s⁻¹. Evaluations were performed at three phenological stages: seedling, juvenile, and adult. Measured parameters included biomass, dry matter content, photosynthetic efficiency (Fv/Fm), total phenolic content, antioxidant capacity, and anthocyanins. Results indicated a cultivar-dependent response; in green basil (GB), R:B ratios of 2:1 and 3:1 significantly enhanced biomass production and photosynthetic efficiency, particularly at advanced growth stages. Conversely, purple basil (PB) exhibited a higher accumulation of bioactive compounds under red-dominant spectra (3:1 and 5:1 ratios). Furthermore, the impact of light quality was dependent on the phenological stage; significant differences were minimal during early stage but became pronounced as plants developed, with higher red light proportions favouring bioactive compound accumulation in the adult stage. These findings highlight the importance of adjusting light recipes according to the specific cultivar and growth stage to optimize both biomass yield and functional quality in vertical farming. • Red-dominant spectra (3:1 R:B) maximized biomass in adult green basil. • Red:Blue 5:1 ratio enhanced total phenolic content in purple basil seedlings. • Antioxidant capacity in purple basil was genotype-dependent, favoring red-rich light. • Dry matter content peaked at the seedling stage regardless of spectral treatment.