This study aimed to investigate the effects of different light quality combinations on the growth and development, photosynthetic physiological characteristics, expression of key flowering genes, and single-plant grain formation in barley (Hordeum vulgare L.), to optimize the light quality ratio, and to achieve a breeding configuration enabling multiple generations per year, so as to promote the application of rapid breeding technology in barley.

Under controlled environmental conditions, two spring-type two-rowed beer barley cultivars, including Hua 22 and Yanmai 3, were cultivated under six LED spectral combinations: white light (W), red light (R, λ_max≈660 nm), blue light (B, λ_max≈450 nm), and red-blue composite lights (1R : 1B, 1R : 3B, and 3R : 1B). The "accelerating effect" of different light quality combinations was comprehensively evaluated using the entropy-weighted TOPSIS method. This evaluation was based on monitoring key developmental stages throughout the entire growth cycle, measuring photosynthetic physiological parameters, analyzing the transcript levels of key flowering genes via quantitative real-time PCR (qRT-PCR), and assessing yield components (number of grains per spike and 1000-grain weight).

Under the white light (W) treatment, although Hua 22 and Yanmai 3 completed a generation cycle within 50 and 44 days, respectively, they exhibited a lower number of grains per plant and a reduced germination rate. In contrast, 3R : 1B light combination ensured rapid barley growth (Hua 22, 56 days per generation; Yanmai 3, 49 days per generation), which also significantly improved the number of grains per spike and seed germination rates. No significant differences were observed in the SPAD value, photosynthetic parameters, or chlorophyll fluorescence parameters between the 3R : 1B treatment and white light treatment. With the increase in blue light proportion, the whole growth period of barley was prolonged, and the SPAD value, photosynthetic parameters, and chlorophyll fluorescence parameters all decreased. qRT-PCR results indicated that light qualities with a high red light ratio accelerated the reproductive process by upregulating flowering-promoting factors, such as HvFT1, HvBM3, and HvAP1, as well as downregulating the flowering repressor HvRAV2-like.

The 3R : 1B light spectrum not only ensured the rapid growth and development of barley but also significantly increased grain yield, achieving optimal multi-generation cycles per year. This study laid a technical foundation for rapid breeding in barley.