Strategic modulation of blue and red light ratios during seedling phase ameliorated cold tolerance of Viola × wittrockiana

The present experiment was conducted to gain a deeper understanding of how spectral composition impacts the anatomical and physiological responses of plants to cold stress. We grew seedlings of Viola × wittrockiana for 28 days under modulation of red-to-blue light ratios, as well as under white LED and fluorescent lamps, before exposing them to cold stress at − 10 °C. The results indicated that spectral composition during the seedling phase significantly affected cold tolerance. Seedlings grown under a gradual increase in red light (70% to 85%) exhibited the highest survival rate (100%), the lowest electrolyte leakage (13.7%), and the smallest changes in the Chl a/b and total Chl/Car ratios (12% and 13%, respectively). In contrast, seedlings grown under white LED light showed the lowest survival rate (69.7%), the highest electrolyte leakage (20.3%), and the greatest changes in Chl a/b and total Chl/Car ratios (151% and 50%, respectively). Furthermore, seedlings exposed to a gradual increase in red light (70% to 85%) produced the highest levels of proline (5.3 µg g⁻¹ FW) and lignin (112 µg g⁻¹ FW), as well as the highest concentrations of the studied antioxidant enzymes. Additionally, lower levels of red light in treatments with constant red-to-blue light ratios hindered enzyme production. In summary, light quality during the seedling phase significantly influenced the cold tolerance of studied plant materials. This method has the potential to enhance the preparation of plant material during the propagation phase, enabling it to better withstand low temperatures.