Effect of light wavelength on soybean growth and development in a context of speed breeding

Soybean [Glycine max (L.) Merr.] breeding involves crossing and inbreeding for multiple generations to develop genetically stable lines. The long generation times cause early generations to be the major bottleneck in soybean breeding. Here we tested the effect of red and blue light (RB) and full‐spectrum white light (FS), coupled with 12‐h light (29 °C) vs. 12‐h darkness (27 °C) photothermal conditions, on the growth and development of soybean lines and breeding materials of diverse maturity groups (MGs) in a context of speed breeding. We observed that RB light vs. FS light reduced plant height but did not affect vegetative biomass, pods and seeds per plants, nor the ability to meet a minimum of one seed per plant. Overall, the RB treatment reduced the interval planting to physiological maturity by 1.5 d vs. the FS treatment. The period between planting and harvest of mid‐ and late‐maturity soybean ranged from 63 to 81 d, vs. ∼120 d observed in field conditions. Also, days after planting (DAP) to R7 was dependent on soybean MG. The use of RB light, coupled with photothermal conditions herein reported, would allow to advance up to five generations of U.S.‐adapted soybean under a controlled environment instead of the one to three generations currently possible. This methodology is simple and easily scalable, for it maintains stable growing conditions throughout the crop cycle and it allows for simultaneous planting and harvesting within the same growth room. This could have a significant impact in genetic gain of U.S. soybean breeding programs.