ASHS 2024 Conference

Speed breeding is a cutting-edge technology, that utilizes controlled environments to significantly reduce plant generation time, thereby accelerating breeding and research programs. The manipulation of temperature, irrigation, phytohormones, and light are the main ways to reduce plant cycles in speed breeding programs. However, changing these factors can result in decreased yield efficiency, which can also affect the quality of a speed-breeding program. This study aimed to increase seed production without increasing harvest time in soybean plants, a short-day plant, by using different photoperiod regimes. Two soybean (Glycine max) varieties, S16-14801C and CZ7570LL, were grown from seeds in 11-L pots containing peat moss-based substrate in growth chambers with controlled temperature (27 ± 0.5 ˚C), CO2 (475 ± 15 µmol mol-1), humidity (70 ± 5.0%), and light (300 ± 5 µmol m-2 s-1 at table; 20% blue, 10% green, 70% red). One week after germination, seedlings were exposed to four different photoperiod regimes: i) 10 h (0 w at 18 h); ii) two weeks at 18 h and then 10 h (2 w at 18 h); iii) four weeks at 18 h and then 10 h (4 w at 18 h) and iv) six weeks at 18 h and then 10 h (6 w at 18 h). The light fixtures were not adjusted over plant height following industry practices. The plants were harvested ten days after 95% of the pods had attained maturity (R8 stage). For both varieties, the number of pods and seeds and seed weight per plant increased linearly, with the increase in the number of weeks at 18 h. Thus, the number of pods, seeds, and seed weight of plants at 6 w at 18 h were at least 5-fold higher than in plants at 0 w at 18 h. Similarly, plants grown at 6 w at 18 h presented 4-fold higher biomass than plants grown at 0 w at 18 h. However, the increased seed yield and biomass accumulation did not result in a longer plant cycle; plants of both varieties at 6 w at 18 h were harvested 32 days before plants at 0 w at 18 h. Here, we demonstrated that seed yield can be increased and harvest time decreased by manipulating the photoperiod. These findings can help plant breeders in identifying the most suitable method for growing soybean plants in a shorter period, while also ensuring high seed production.