Evaluation of tomato seedlings growth response under different qualities of supplemental LED light

Tomato seedlings (Solanum lycopersicum 'Siranzo') were grown using supplemental LEDs (light emitting diodes) light to evaluate growth, physiological and morphological responses. Plants were sown on peat in a glass-glazed greenhouse at in Bologna, Italy (44 degrees 29'38"N, 11 degrees 20'34"E). Two monthly experiments were performed during spring season: first experiment from March until April 2021 (Exp. I) and second experiment from May until June 2021 (Exp. II). Supplemental LED lighting treatments were applied from sowing and consisted in red and blue (RB) (ratio=3), red and blue (ratio=3) + far-red (FR) the whole day, and red and blue (ratio=3) + far-red at the end-of-day (EOD). All treatments were applied for 16 h d(-1) (h 8-00) with an intensity of 180 mu mol s(-1) m(-2). Control seedlings (CK), grown under natural light only, were also considered. The results showed a variable growth and morpho-physiological response of seedlings depending on lighting treatment. In particular, RB and FR treatments demonstrated to improve plants compactness, contemporarily guaranteeing a good photosynthetic performance. Among treatments supplied with artificial lighting, EOD plants presented longer hypocotyls. Finally, CK plants presented longer hypocotyls, higher leaf area and lower chlorophyll content, possibly as a response to light shortage.