2018 ASHS Annual Conference

A greenhouse study was conducted to examine the effects of supplemental ultraviolet light (UV-A and UV-B) on the nutritional quality of lettuce (Lactuca sativa L. ‘New Red Fire’ and ‘Two star’), spinach (Spinacia oleracea ‘Bloomsdale’) and tomato (Solanum lycopersicum L. ‘BHN-589 F1‘). Three-week old plants were transferred to a greenhouse and grown under full sun with supplemental UV light. The plants were exposed to UV just prior to harvest and nutritional quality was determined by mineral nutrient composition and phytochemical content in edible parts of the plants. The plants were subjected to UV treatment consisting of UV-A (8.11 W/m²), UV-B (1.97 W/m²), UV-A+UV-B (5.08+1.55 W/m²) for various lengths of time. Supplemental UV did not affect the biomass accumulation, leaf area or the leaf-shape index in green-leaf lettuce (Two Star). However in red-leaf variety (New Red Fire), UV-B and UV-A+UV-B suppressed leaf area, but not the biomass accumulation compared to UV-A treatment and the control. In addition, the total phenolic content and antioxidant capacity in red-leaf variety were significantly higher under UV-A compared to the control, although there were no significant differences in green-leaf variety. UV increased the leaf concentration of Ca and Mg in both varieties of lettuce, and N only in green-leaf variety. Similar response was observed in spinach where UV increased Ca, Mg and N levels along with P, S and Cu. However, no significant increase in phytochemical content was observed. While N content of green-leaf varieties (in both leafy vegetables) increased there was a significant decrease in carbon accumulation in response to UV exposure. With regard to tomato fruits, UV exposure did not significantly affect the fruit yield or the total phenolic content. The results show that the UV effect on growth and nutritional quality among leafy vegetables is quite variable, and thus, further analyses with regard individual phenolic and carotenoid compounds are being conducted.