Plant breeding is a key element for future agricultural production that needs to cope with a growing human population and climate change. However, the process of developing suitable cultivars is time-consuming, not least because of the long generation times of crops. Recently, speed breeding has been introduced for long-day crops, but a similar protocol for short-day crops is lacking to date. In this study, we present a speed breeding protocol based on light-emitting diodes (LEDs) that allow to modify light quality, and exemplarily demonstrate its effectiveness for the short-day crops soybean (Glycine max), rice (Oryza sativa) and amaranth (Amaranthus spp.). Adjusting the photoperiod to 10 h and using a blue-light enriched, far-red-deprived light spectrum facilitated the growth of short and sturdy soybean plants that flowered ~ 23 days after sowing and matured within 77 days, thus allowing up to five generations per year. In rice and amaranth, flowering was achieved ~ 60 and ~ 35 days after sowing, respectively. Interestingly, the use of far-red light advanced flowering by 10 and 20 days in some amaranth and rice genotypes, respectively, but had no impact on flowering in soybeans, highlighting the importance of light quality for speed breeding protocols. Taken together, our short-day crops’ speed breeding protocol enables several generations per year using crop-specific LED-based lighting regimes, without the need of tissue culture tools such as embryo rescue. Moreover, this approach can be readily applied to a multi-storey 96-cell tray-based system to integrate speed breeding with genomics, toward a higher improvement rate in breeding.
Figure 1: Development of a speed breeding protocol for soybean. a Schematic overview of the steps to be optimized: the time to flowering and to maturity. b LED light spectrum with four separately controllable channels and impression from inside a LED speed breeding box. c Soybean grown under short-day and long-day conditions. Scale bar = 10 cm. d Bar plots showing the effects of day length on flowering time and plant height under blue, green and red light conditions. e Effect of red and far-red light on plant morphology. Scale bar = 10 cm. f Flowering time and plant height dependent on different ratios between red and blue light. g Germination rate of soybean seeds harvested at different time points. h Effect of light intensity on germination rate at 63 days after sowing