Friend or Foe: Exploring the impact of UV-B irradiation in seedling stage and its subsequent effects on growth, quality and yield of lettuce plants

Solar ultraviolet-B (UV-B) radiation plays a crucial role in modulating plant growth, development and various physiological processes. While terrestrial life is adapted to natural UV-B levels, elevated amounts of UV-B reaching the Earth’s surface may have positive and negative effects on biological systems, depending on intensity and duration. This study aimed to explore the effects of early stage UV-B exposure on plant growth, physiology, yield and nutritional quality in two lettuce cultivars and to examine the subsequent responses at harvest. The seedlings of curly lettuce (Lactuca sativa var. crispa 'Caipira') and iceberg (Lactuca sativa var. capitata 'Fortunas') were exposed to 4.8 kJ · m⁻² and 9.6 kJ · m⁻² UV-B for 12 consecutive days, then transferred to soilless culture systems for further growth and evaluation at harvest. The supplemental UV-B irradiation led to significant changes in plant height, root length, leaf Soil Plant Analysis Development (SPAD), hue angle, calcium and iron contents of both cultivars in the seedling stage, whereas only lightness, calcium, potassium, zinc and copper contents were affected at the maturity stage. While moderate UV-B levels had no adverse effect on marketable yield or head weight, the higher dose negatively impacted yield parameters. These findings suggest that carefully calibrated UV-B exposure during early growth can potentially be used to manipulate physiological and biochemical traits beneficial to market value and nutritional quality. Moreover, UV-B may serve as an alternative to chemical growth retardants commonly used in nurseries. Future studies should focus on molecular, genetic and transcriptomic mechanisms underlying UV-B-induced changes.