Effects of Photoperiod and Carbon Dioxide Concentration during Transplant Production on Floral Development and Bolting of Spinacia oleracea L.

The effects of photoperiod and CO2, concentration on the bolting of Spinacia oleracea transplants were investigated. Shoot and root dry weights of the transplants increased significantly with increasing CO2 concentration. The floral development of transplants grown under a 14-h·d-1 photoperiod were more progressed than those grown under a 10-h· d-1 photoperiod. However, the progress of floral development was similar for the transplants grown under different CO2 concentrations if the photoperiod was the same. More than 80% of the plants in the treatments with the 14-h·d-1 photoperiod bolted 3 d after transplanting (DAT), while none of the plants in the 10-h·d-1 treatments bolted at this time. At harvest (14 DAT) the percentage of the plants that bolted was greater than 80% in all treatments. Between treatments with the same CO2 concentration, the flower-stalk length of plants at harvest in the 14-h·d-1 photoperiod treatment were greater than those in the 10-h·d-1 treatment. Among plants in the same photoperiod treatment, flower-stalk lengths were not significantly affected by CO2 concentration after they were transplanted to a 16-h·d-1 photoperiod. These results show that the delay of bolting that occurs with shortening the photoperiod during transplant production was due to the delay of floral development and not to retarded vegetative growth.