Red–blue light ratios shape growth, physiological responses and leaf metabolic profiles in tissue-cultured Zingiber officinale plantlets

Light quality regulates in vitro plant development, but the integrated responses of ginger plantlets to different red–blue light ratios remain unclear. Tissue-cultured Zingiber officinale Roscoe plantlets were exposed for eight weeks to white light (W), red light (R), blue light (B), or combined red–blue light at 1:1 (RB11), 1:3 (RB13), or 3:1 (RB31). Morphological traits, physiological and biochemical parameters, and untargeted leaf metabolic profiles were analysed. R primarily promoted stem elongation (mean stem length 46.0% higher than W) but produced relatively fewer buds, leaves and roots. B increased soluble sugar and protein contents and produced the lowest malondialdehyde level (19.7% below W). RB31 showed high catalase and peroxidase activities together with relatively low malondialdehyde. RB13 produced the highest bud and root numbers (root number 21.3% above W), maintained a high leaf number, enhanced carotenoid accumulation, and was associated with candidate responses involving lipid, phenylpropanoid, flavonoid, glutathione, polyamine and carbon–nitrogen metabolism. Only linoleic acid metabolism in B versus W remained significant after false discovery rate correction. Overall, the treatments induced distinct growth, physiological and metabolic response patterns. RB13 showed the most balanced response among the combined red–blue treatments and may be suitable for improving in vitro ginger plantlet quality.