Morphological and physiological response in green and purple basil plants (Ocimum basilicum) under different proportions of red, green, and blue LED lightings

Abstract

Light quality not only influences the accumulation of photosynthetic pigments, but also mediates photo-physiological parameters in plant leaves. There is limited information available regarding the photosynthetic physiology of Ocimum plants under the influence of different light spectra. Monochromatic light spectra have been used for studying morphological and phytochemical productions of these plants. However, different proportions of red and blue light irradiation and supplement it with green light to identify the optimized light quality conditions for growing basils remain unknown. The aim of this study was to investigate that modifying the spectral environment with light-emitting diode (LED) lighting in hydroponic growth chambers can alter growth patterns in basil leaves and plant morphology, affecting physiological performance and photosynthetic pigments in the leaves of both green and purple basils. Plants were hydroponically cultured with a 12 h photoperiod at 24/20 °C (day/night), 75 % relative humidity, and 180 μmol m−2 s−1 photon flux density under three LED sources and three spectral color ratios, red (R): green (G): blue (B) = 4: 1: 1, 2: 1: 1, and 1: 1: 1, in an environmentally controlled growth room for 64 d after sowing. These various spectral environments affected plant growth, leaf area, and shoot and root fresh and dry weights, as well as the plant shape of both species. Plants treated with a 4:1:1 ratio were significantly larger than plants treated with a 1:1:1 ratio, demonstrating that the former light quality can be strategically used to enhance the growth of basil plants. Furthermore, 4:1:1-treated plants had relatively higher photosynthetic capacity, quantum yield, and photosynthetic electron transport compared to 2:1:1 or 1:1:1 treatments. Light treatments significantly and obviously affected pigments and cultivars differently, in that purple and green cultivars displayed remarkably higher and lower pigment content under 1:1:1 and 2:1:1 treatment, respectively. The precise management of photosynthetic parameters in response to the spectral quality of lighting may hold promise for maximizing the economic efficiency of the growth, development, and metabolic potential of O. basilicum plants grown in controlled environments.