A Scheme for Speed Breeding of Tomato Through Modification of the Light Environment

This study aimed to determine optimal light recipes for speed breeding of tomato (Solanum lycopersicum L.) in a plant factory. Two tomato cultivars, Zuanhongmeili and Xiaokeai, were investigated. In Experiment 1, conducted under a 12 h photoperiod, both cultivars showed accelerated development with increasing light intensity. The optimal light intensity range of 300–400 μmol·m−2·s−1 promoted development and seed maturation. Under these conditions, Zuanhongmeili and Xiaokeai achieved flower bud emergence in the shortest times, at 24.91 ± 0.13 and 24.91 ± 0.12 days after sowing (DAS), respectively. Furthermore, for the two cultivars, anthesis initiation occurred at 39.08 ± 0.62 and 35.78 ± 0.19 DAS, fruit setting at 41.31 ± 0.61 and 38.54 ± 0.24 DAS, and the breaker stage at 83.05 ± 1.05 and 69.78 ± 0.29 DAS, respectively, under these conditions. Critically, germinable seeds were harvested from each cultivar as early as 63 and 60 DAS, projecting a theoretical annual generational turnover of up to six cycles. Based on these results, a baseline irradiance of 350 μmol·m−2·s−1 was selected for Experiment 2, which independently assessed the impact of photoperiod. Zuanhongmeili and Xiaokeai both showed accelerated development with increases in photoperiod. The optimal photoperiod of 20 h promoted development and seed maturation. Under a 20 h photoperiod, Zuanhongmeili and Xiaokeai achieved flower bud emergence in the shortest times, at 25.12 ± 0.09 and 23.76 ± 0.13 DAS, respectively. Furthermore, anthesis initiation occurred at 41.21 ± 0.66 and 37.27 ± 0.34 DAS, fruit setting at 44.51 ± 0.15 and 40.25 ± 0.08 DAS, and the breaker stage at 91.19 ± 0.59 and 77.47 ± 0.36 DAS, respectively, under these conditions. The shortest times to harvest of germinable seeds from the two cultivars in this experiment were 76 and 72 DAS. Overall, this study demonstrates that tailored light environments, particularly the light intensity regime identified in Experiment 1, can dramatically accelerate tomato growth and development, enabling production of six generations per year in a controlled environment.