Purple-leaf lettuce cultivar seedling production under different light treatments

Abstract

One of the major challenges in the production of lettuce (Lactuca sativa L.) seedlings is to get quality seedlings, which can be difficult in conditions of low light. This paper aimed to study the effects of multispectral white and monochromatic blue light- emitting diodes (LEDs) lighting on development and chlorophyll content in Viola curly purple-leaf lettuce cultivar seedlings, compared to standard cultivation in greenhouses. The research was performed in December 2023/January-February 2024 at the Institute for Vegetable Crops Smederevska Palanka, Serbia. Seeds were sowed in containers filled with commercial substrate. In the phase of three leaves, six containers with plants were placed in phytochambers (three containers per LED), while three containers were kept in the greenhouse for control. Plants were cultured in phytochambers for 25 days with a 9/15 h and 10/14 h (light/dark) photoperiod, to simulate outdoor conditions. Morphological growth parameters were measured after 11 and 25 days, while chlorophyll content was measured after 4, 11, 18 and 25 days. Results of this study show that plants' morphological parameters and chlorophyll content were significantly influenced by LEDs. During lettuce cultivation in phytochambers, it is necessary to be cautious regarding lighting duration. Our results indicate that extended exposure to LEDs negatively affects Viola lettuce seedlings' development, leading to plant elongation and deformation. Such seedlings are not able to grow into healthy and quality plants. Additionally, extended artificial illumination affects one of the most advantageous traits of the Viola lettuce cultivar - purple leaves. Exposure to LEDs for more than 10 days leads to the loss of anthocyanin, and accordingly purple color in leaves. In order to produce quality seedlings, we recommend exposing Viola lettuce cultivar seedlings to monochromatic blue and multispectral white LEDs only for four and 10 days, respectively.