Manipulation of bolting and flowering in spinach (Spinacia oleracea L.) transplant production system using artificial light

The spinach (Spinacia oleracea L.) transplants were produced with artificial light under short day and low temperature conditions, namely, 8-hour (treatment AL8H) and 12-hour (treatment AL12H) lighting periods, were compared with the transplants produced by conventional methods under natural long day and high temperature conditions (treatment ND15.5H). The transplants produced with artificial light in the new method showed a uniform and competitive growth. To see their bolting characteristics, a major problem in spinach production in summer, the transplants were transplanted in a hydroponic system in a greenhouse. At 14 days after transplanting, about 5 % of the spinach plants bolted in the artificial lighting treatments with a flower stalk length of 0.3 cm, which was not considered to decrease the market value of spinach. On the other hand, 85 % of the spinach plants in treatment ND15.5H lost their market value with a flower stalk length of 2.8 cm. Considering that this experiment was done from mid July through mid August in Japan, the spinach transplants produced in the new method would not bolt before they are harvested in any season of the year. In this study, it was found that bolting could be prevented by manipulating daylength and temperature during the transplant production process. These results suggest that the transplant production business is also feasible for other leafy vegetables that have bolting and flowering characteristics similar to those of spinach because of its ability to produce high quality transplants.