Light modification by color nets improve quality of lettuce from summer production

The effects of utilization of different color shade nets in lettuce production during the summer season were evaluated in Serbian climate conditions for pearl, blue, red and black shade nets in comparison to open field production. Applied shade nets (with shade index of 50%) significantly reduced solar irradiation (from 890 in open field to 400-560 Wm(-2) under the shade nets) and photosynthetically active radiation (from 2020 in open field to less than 1000 mu mol s(-1) M-2 under the shade nets). Color shade nets affected both, properties of lettuce during the growing period and its morphological properties. Namely, the leaf area index was increased, lettuce heads were characterized with significantly higher marketable head weight and head diameter, the period from planting to bolting was significantly shorter, the outer leafs were characterized with more intensive green tone (-a*) and the lettuce leafs were softer and more tender for lettuce grown under the shade nets in comparison to open field production. In respect to lettuce composition, total chlorophyll content, contents of both chlorophyll a and chlorophyll b, as well as carotenoid content were significantly higher in shaded leaves of lettuce than in the control plants. Significantly higher (30.78 mg GAE g(-1) d.m.) total phenol content was determined in plants grown under the pearl shade nets accompanied with significantly higher flavonoids content (14.28 mg RE g(-1) d.m.) and significantly higher antioxidant properties (lower EC50 DPPH values) in comparison to all other nets. However, the antioxidant properties of control plants were at the same level as for the pearl net, in spite of lower phenols and flavonoids content.