Impact of light quality on accelerating soybean speed breeding efficiency using LED-based systems

Traditional soybean (Glycine max (L.) Merr.) breeding is time-consuming, often requiring 6–12 years to develop new cultivars due to lengthy cycles and low efficiency. Speed breeding offers a promising solution to accelerate genetic advancement; however, studies optimising light quality for soybean remain limited. This study evaluated two light-emitting diodes (LEDs) setups, blue (BL) LED light in a growth room and red-white (RW) LED in a speed breeding chamber, on soybean growth, reproductive traits, and yield parameters. Four accessions were tested under 8-h light (31.6 ± 4.7 °C) and 16-h dark (24.5 ± 2.3 °C) cycles. The BL LED light provided an intensity of 231.1 µmol photons m−2 s−1, while the RW LED delivered a light intensity of 513-µmol photons m−2 s−1. RW significantly reduced time to flowering (29–33 days) and maturity (66–72 days), compared to BL LEDs (33–38 days) to flowering, (90–95 days) to maturity, and field conditions (~ 91–103 days). RW LED reduced generation time by 24–31 days compared to field conditions. Moreover, significant differences were observed in plant height, pod number, and seed yield between treatments, while stem thickness and number of trifoliate leaves remained unchanged. Additionally, freshly dried seeds exhibited high germination rates (83.33–100%), confirming seed viability under rapid cycling. This optimised protocol, utilising RW LED light with an 8-h photoperiod and harvesting at the R6 growth stage (pod-filled), highlights the critical role of light quality in accelerating soybean breeding and provides a refined strategy to enhance breeding efficiency in controlled environments.