The Effect of the Light-Emitting Diode Spectrum Compared to the Greenhouse Natural Light on the Quality of Solenostemon escutellariodes 'Wizard Scarlet' and Petunia × hybrida 'Scarlet Eye' Transplant

The light is not only a photosynthesis energy source but also is a plant growth and development stimulation from germination to flower initiation process. The light quality plays an important role in all steps of growth process particularly in photosynthesis and morphological properties of plant species. Studies have reported that, LEDs present the maximum PAR efficiency among artificial lighting systems. LED lamps contribute to energy saving by 75 and 30 percent as compared to incandescent light bulbs and fluorescent lamps, respectively. LEDs emit blue, red, orange, yellow, green, red, and infrared light and can be used as a hybrid spectrum. For these reasons, an experiment was conducted to investigate the effect of quality of LED light on morphological and physiological characteristics of Solenostemon and petunia.

Research experiments were conducted on Solenostemon escutellariodes ‘Wizard Scarlet’ and Petunia × hybrida ‘Scarlet Eye’ in a completely randomized design with three treatments of different light quality and 10 replications. The seeds were planted in 105-cell seedling trays and in a mixture of 70% peat moss and 30% perlite. Seedlings were grown in natural greenhouse (control) and LED (50% blue + 50% red and 100% white light). The light intensity was 60 ± 5 µmol.m-2.s-1 for LEDs and the daily greenhouse cavity was 5 ± 14 µmol.m-2.d-1. Since the main goal of the study was to compare the effect of LED light quality with sunlight in conventional greenhouse conditions. The LED treatments were applied from the germination until seedling production stage in a growth chamber with the light/dark regime of 18/6 hours, 23±1°C temperature, and 50±5% relative humidity. While, their tray in the greenhouse with 55±5 mol.m-2.d-1 DLI, 21±5°C average daily temperature and 50±5% relative humidity (Data logger 8808 temp. + RH) were regarded as the control treatment. After eight weeks, the morphological and physiological traits were recorded. Finally, the data were statistically analyzed with SAS (9.4) software package, and the means were compared by LSD test at p < 0.05 level.

At the end of study, some morphological and physiological traits were evaluated. The results showed that the leaf area average (3.63 cm2), height (5.04 cm), internode length (18.62 mm), stem diameter (2.52 mm), shoot fresh weight (1.74 g) and chlorophyll fluorescence (0.83) of Solenostemon seedlings in 100% white light were more than 50% blue + 50% light green and greenhouse light. Also, the highest leaf area temperature (27.4 ° C), total chlorophyll (0.8 mg g-1 fw) and carotenoids (2.229 mg g-1 fw) were related to control treatment and the highest number of leaves (21), shoot dry weight (0.165 g), fresh (1.65 g) and root dry weight (0.114 g) were observed in 50% blue + 50% red light composition. According to the results of petunia, white LED light increased leaf area (1.74 cm2), shoot fresh weight (0.51 g) and root dry weight (0.03 g). The leaf surface temperature (26 oC) and total chlorophyll content (1.44 mg g-1 fw) in the control group were higher than the other treatments, and the carotenoids content (3.12 mg g-1 fw) was obtained in 50% red + 50% blue LED. The leaf surface temperature and total chlorophyll content in greenhouse light were higher than other treatments and the highest carotenoids (3.119 mg / g) were obtained from 50% red + 50% blue LED.

Light quality has a great impact on the growth and development of plants and is a powerful tool for controlling various processes .The results showed that different light sources with different qualities had different effects on different plant species and that LEDs could replace natural light in growing chambers and in areas where light was insufficient. Due to the increased quality and reduced transplant losses in the transplant phase and their low utilization, they are justified in terms of production costs. It should be noted that in addition to light; temperature, humidity and other environmental factors are also effective in transplant production. Based on the measured indices in Solenostemon, it can be concluded that the red + blue LED light transplanting stage is superior to other treatments. In petunia, white LED treatment caused the highest shoot and fresh and dry weights of roots and leaves respectively. Like Solenostemon, the highest chlorophyll and leaf surface temperatures were related to the control treatment and was superior to the petunia transplant in terms of the sum of measured indices of white light treatment.