Gradual modification of the light spectral combinations during the growth of Petunia×hybrida seedlings improves vegetative growth traits and accelerates flowering

Due to the effect of some wavelengths of light such as blue and red on the structure and activity of different plant pigments, in recent years, different ways of using LED lamps in plant breeding environments and in order to Improve plant growth have been studied. In this study, we aim to investigate how gradual changes in spectral distribution compared to constant spectral distribution, fluorescent light, and high-pressure sodium lights affect the vegetative growth traits of petunia seedlings, energy use efficiency during the seedling growth and the change in the reproductive behavior of mature plants. Petunia seedlings were affected by different spectral distributions for 28 days. In some light treatments. In some light treatments (85%red: 15%blue, 70%red: 30%blue, and 55%red: 45%blue) while in others, the percentages of blue and red lights changed gradually according to the schedule which included a gradual increase in the amount of red light or a gradual decrease in the amount of red light. Also, the effect of fluorescent lamps (control) and high-pressure sodium was studied. At the end of the seedling stage, samples of the lighting treatments were transferred to a greenhouse with completely identical environmental conditions to determine the effect of different spectral distributions during the seedling stage on the vegetative and reproductive growth of mature plants. The results showed the improvement of the studied growth traits under the gradual changes of spectral distribution during the seedling stage. The dry weights of shoot and root, leaf area, number of leaves, contents of chlorophyll and carotenoid pigments, and energy use efficiency were significantly higher under the lighting treatment which was initially monochromatic blue light, and then the amount of red light was gradually increased. Also, it was observed that the vegetative growth and flowering of mature plants were affected by the spectral distribution used during the seedling stage. Mature plants whose seedlings were under the influence of monochromatic blue light at the beginning of their growth and the amount of blue light was gradually reduced, had a higher fresh and dry weight of shoot and root, root volume, number, and length of lateral branches. Compared to other plants, they were plants. It was also observed that although changes in the spectral composition of light during seedling growth had a significant effect on the flowering time of mature plants, there was not a significant difference between some light treatments (constant ratio of 45% blue: 55% red, high-pressure sodium lamp light and a gradual increase in the amount of red light). Modifying the spectral combinations during the seedling stage influenced their vegetative traits of them. Additionally, lighting treatments during the seedling stage affected the vegetative traits of mature plants. Further, the gradual changes in the blue and red-light proportion in spectral distribution significantly affected the energy use efficiency, which affects the reasonable economic achievements in plant production. Lighting systems could be applied to plant production differently in the future, according to the results of this study.