Indoor green and purple lettuce seedling production under LED lights

In the Balkans' agroecological conditions, early seedling production occurs during winter. The quality and duration of sunlight during this period are suboptimal, preventing the seedlings from reaching their full genetic yield potential due to the deprivation of certain light qualities. Therefore, our study aimed to test whether the usage of energy-efficient light-emitting diodes (LEDs) can fulfill the plants' light requirements during the early stages of seedling production. The research was performed at the Institute for Vegetable Crops Smederevska Palanka, Serbia. We used three commercial lettuce (Lactuca sativa L.) cultivars—Genesis, Jukebox, and Viola—for the experiment. In the three-leaf stage, plants were placed in plant growth chambers and exposed to multispectral white (W) and monochromatic blue (B) LEDs for 25 days with a 9/15h and 10/14h (light/dark) photoperiod, to simulate outdoor conditions. Cultivation in a greenhouse using only natural daily light (DL) served as the control. After 25 days, morphological growth parameters such as root and shoot weight were measured. Additionally, the total chlorophyll content was determined spectrophotometrically using the method described by Lichtenthaler. Our results showed that compared with the control, W and B LEDs significantly increased the seedling root and shoot weight, while B LEDs increased the total chlorophyll content. In plants grown under DL and W LEDs, the total chlorophyll content did not differ significantly. The Jukebox genotype exhibited the strongest response to the light treatment. This genotype had the highest total chlorophyll content, as well as shoot and root weight under B LEDs compared to W LEDs and DL. When exposed to B LEDs, the Jukebox genotype reached a shoot and root weight up to 4 times that of to DL. Based on our results, this lettuce cultivation method enhances seedling growth and chlorophyll content and positively affects seedling quality.