Influence of red:blue ratio in LED lighting for indoor cultivation of edible marigold flowers

Edible flowers are becoming increasingly important for human consumption due to their capability to make food more attractive and tastier. Furthermore, edible flowers are receiving renewed interest from consumers as a source of bioactive compounds with beneficial health effects. LED lighting technologies are gaining increasing relevance as they allow indoor plant cultivation, where both environmental parameters and lighting characteristics can be effectively adapted to plant needs, promoting flower induction and plant productivity. In the present study, five LED light treatments characterized by varying red:blue (RB)ratio (RB0.5, RB1, RB2, RB3, RB4) were compared for their effects on both the growth and morphogenesis of marigold (Calendula officinalis L.). Cool fluorescent light (FL) was also considered as control. Marigold plants were cultivated in growth chambers (24°C, 60% RH) and supplied with a Photosynthetic Photon Flux Density (PPFD) of 215 µmol m-2 s-1 with a photoperiod of 16 h d-1. Flower induction was increased by LED lighting as compared with control, reaching maximum values under RB≥2. Flower production (g plant-1) was also affected by changes in light spectrum, with the highest values in plants grown under RB≥2. Significant variations on the energy use efficiency (expressed as the electricity requirements per unit of fresh flower produced) were also associated with changes in RB ratio.