Effects of LEDs Light Spectra on the Growth, Yield, and Quality of Winter Wheat (Triticum aestivum L.) Cultured in Plant Factory

The light-emitting diodes (LEDs) are expected to be effective light sources for growing wheat in indoor cultivation due to their small size, long lifespan, high safety performance, and customized wavelengths. In the present study, the influences of LEDs light sources with different spectra combinations were investigated in wheat plants grown in hydroponic system. Eight types of different spectra were compared: white light (W), white–green light (W:G = 4:1, W4G1), red–green light (R:G = 4:1, R4G1), red–green–blue light (R:G:B = 4:1:1, R4G1B1), and four types of red–blue lights (R:B = 3:1, R3B1; R:B = 2:1, R2B1; R:B = 1:1, R1B1; R:B = 1:6, R1B6). The growth and development were monitored together with the activity of antioxidant enzymes in leaves. In addition, grain yield and quality were also investigated. The results showed that winter wheat could complete its life cycle under all eight LEDs light regimens in the completely enclosed hydroponic cultivation environment. Among them, plants in W, W4G1, and R4G1 grew fastest, followed by those of R4G1B1 and then by those of R3B1, R2B1, R1B1, and R1B6. Although blue light increased tillering number and dry matter production of whole plant, it was not conducive to distribution of dry matter to spikes and grain yield per plant. On the contrary, red light was positively correlated with dry matter distribution and accumulation in spikes. In addition, green light was helpful for the percentage of earbearing tiller, which constituted the number of spikes. Wheat grown in R4G1 had the higher spike number per plant, grain number per spike, and grain weight, leading to the highest grain yield per plant and harvest index. Meanwhile, the starch content, protein content, as well as the nutritional quality and processing quality of wheat flour grown under R4G1 could reach moderate levels. Taken together, appropriate LED’s light spectra, such as R4G1, are efficient for wheat cultivation in a controlled environment and make it possible to achieve faster, more, and better winter wheat production.