Investigating growth, root development, and chlorophyll fluorescence of tomato scions and rootstocks under UV-B stress in a plant factory with artificial lighting

Plant factories with artificial lighting (PFALs) provide a controlled environment for seedling production, helping overcome challenges posed by fluctuating weather conditions. UV-B irradiation enhances plant physiology by increasing flavonoid accumulation, strengthening disease resistance, and improving seedling vigor. However, because of species specific and context dependent responses, researchers must further investigate the appropriate timing and dosage of UV-B exposure. Herein, we aimed to determine the optimal UV-B irradiation timing and dose for tomato scions and rootstocks in PFALs. We categorized the irradiation period into three stages ST1 {3–7 days after sowing (DAS)}, ST2 (8–12 DAS), and ST3 (13–17 DAS) and tested doses of 1.44, 2.88, and 5.76 kJ·m⁻²·d⁻¹. At ST2, the 5.76 kJ·m⁻²·d⁻¹ dose reduced plant height by 2.3 cm (28 %) in scions and 4.5 cm (34 %) in rootstocks compared with the control. In the rhizosphere, higher UV-B doses inhibited root development, whereas ST3 1.44–2.88 kJ·m⁻²·d⁻¹ promoted growth. Scions exposed to ST2 5.76 kJ·m⁻²·d⁻¹ showed a 2.3 % increase in dry matter content compared to the control, reaching 9.5 %. The compactness of the rootstock increased to 6.4 mg·cm⁻¹ under conditions of ST2 2.88 kJ·m⁻²·d⁻¹, 1.9 mg·cm⁻¹ (42 %) increase compared to the control 4.5 mg·cm⁻¹. Chlorophyll fluorescence parameters reflected stress responses: F_V/F_M and PI_ABS significantly decreased at ST3 5.76 kJ·m⁻²·d⁻¹, whereas DI₀/RC significantly increased. These results demonstrate that carefully adjusting UV-B timing and dosage can help reduce plant damage and regulate growth, supporting the production of high-quality tomato seedlings in PFALs.