2019 ASHS Annual Conference

Very little is known with regard to the effects of ultra violet (UV) light on the nutritional quality of crops, especially as it relates to the health-promoting phytochemicals. In this study, we examined the effect of supplemental UV using conventional and LED sources on the nutritional quality of lettuce (Lactuca sativa L., red-leaf variety ‘New Red Fire’ and green-leaf variety ‘Two Star’). The plants were grown in a greenhouse and subjected to UV-A, UV-B and UV-A+B (8.11, 1.97 and 5.08+1.55 W/m², respectively) using conventional source (fluorescent tubes) one week prior to harvest. In a separate experiment, plants were grown in a growth chamber set at 22^oC with a PPFD of 244 umol.m^-2.s^-1 (PAR) for 12 h and were subjected to various LEDs equipped with filters to modulate the dispersion of radiant energy one week before harvest. The LED treatment included standard LED and LED with 5-degree lens and LED with scatter lens with mean irradiance of 1.11W/m². UV LED treatments did not show a consistent impact on the accumulation of mineral nutrients and phytochemicals. Use of specific wavelengths of UV (375 and 395 nm) as a supplemental source also did not have a significant impact on the nutrition quality of lettuce. However in contrast, conventional source of UV had significant effect on the accumulation of mineral nutrients and phytochemicals. N accumulation in the leaves of ‘Two Star’ was increased by the exposure of plants to UV-A and UV-B while carbon accumulation was increased by UV-A but was depressed by the exposure to UV-B. In addition, the accumulation of many mineral nutrients such as Ca, Mg, Cu, Mn and Zn were enhanced by exposure to UV-A and UV-B in both varieties. With regard to phytochemical accumulation, UV-A had a stronger response in the red-leaf lettuce variety (‘New Red Fire’) as illustrated by higher accumulation many flavonoids including luteolin 7-glucoside, apigenin 3-glucoside and quercetin 3-glucoside. UV-A treatment generally increased both the total phenolic content and the antioxidant capacity in the leaves of ‘New Red Fire.’ The results show that conventional source of UV has significant positive impact on the nutritional quality of lettuce and particularly, UV-A which can enhance the accumulation of several flavonoids in the leaves of red-leaf lettuce variety.

The study was supported by a grant from USDA-NIFA.