Healing and acclimatization are critical in vegetable grafting under controlled environments. Here, we investigated the impacts of LED light qualities on the morphological traits and photosynthetic performance of grafted tomato seedlings. Seeds of the tomatoes “DRW 7806 F1” and “Maxifort” (Solanum lycopersicum × Solanum habrochaites) used as scion and rootstock were planted in 104-cell plug trays into a mixture of cocopeat and perlite (volume ratio: 3 to 1). Survival ratio, above- and underground growth, photosynthetic performance, soluble carbohydrate content, pigmentation, and antioxidant enzymes activity were evaluated following 20 days of exposure to different light qualities, including white (35% B, 49% intermediate spectra, 16% R) light as control, blue, red, and a combination of red (68%) and blue with the same light intensity of 75 ± 5 µmol m⁻² s⁻¹. The lowest scion diameter, leaf area, root and shoot dry weight, SPAD value, and the highest scion length and amount of soluble carbohydrate were detected in R-exposed seedlings. Moreover, R-exposed seedlings showed leaf epinasty and reduced photosynthetic performance. On the other hand, RB-exposed seedlings showed the highest leaf area, shoot and root dry weight, plant fresh and dry weight, scion stem diameter and photosystem II efficiency. In addition, superoxide dismutase activity was increased in R-exposed seedlings, while guaiacol peroxidase activity was enhanced in seedlings grown in RB. In conclusion, a combination of R and B is suggested as the suitable light spectrum to promote plant growth and photosynthetic performance in grafted tomato seedlings.

Light quality is a critical determinant in controlled environment agriculture, yet information regarding the interactive effects of spectral composition and grafting on tomato seedling performance remains limited. Moving beyond the assumption that rootstock vigor is solely a static trait, we hypothesized that above-ground spectral cues significantly modulate rootstock efficiency. We investigated the synergistic effects of grafting ( Solanum lycopersicum ‘Maxifort’) and various LED spectra (monochromatic Red, Blue, White, and Red:Blue 70:30) on morphological architecture, photosynthetic potential, and the stoichiometric balance of mineral nutrients in tomato seedlings. Our results reveal a critical interaction: while grafting alone alleviated specific nutritional deficits (N, K, Mg) under suboptimal monochromatic red light, the rootstock’s capacity to maximize the uptake of key elements—particularly phosphorus and calcium—was fully realized only under the synergistic Red:Blue spectrum. This study provides empirical evidence that integrating the R70:B30 spectrum with grafting not only improves growth but also optimizes resource acquisition. These findings offer a novel approach to optimizing transplant quality and establish a robust protocol for producing resilient transplants in modern nurseries. Future research should focus on unraveling the molecular pathways underlying this light-rootstock communication.