The aim of this study was to determine the optimum photoperiod of supplemental lighting to obtain high fruit yields in forcing culture of strawberry. Strawberry plants were illuminated with supplemental lighting provided by high-irradiance light-emitting diodes with photoperiods of 24, 16, 14, or 12-h daily under the controlled air temperature conditions set the ventilation starting temperature at 26°C and minimum air temperature at 6°C from October to May. Compared with plants in the other treatments and the control, those in the 12-h photoperiod treatment showed a significant increase in leaf photosynthesis and earlier differentiation of flower buds on the second inflorescence. These physiological changes resulted in the large amounts of carbon translocation from leaf to fruit, leading to the fruit quality improvement and the highest marketable yield among all of the treatments. When the photoperiod of supplemental lighting exceeded 12 h per day, flower opening on the first inflorescence was accelerated, but flower bud initiation on the second inflorescence was inhibited. This inhibition caused a decrease in leaf photosynthesis, leading to excessive carbohydrate accumulation in the leaves, resulting in lower total fruit yield than that from plants in the 12-h photoperiod treatment. These data show that a 12-h photoperiod of supplemental lighting is appropriate to obtain high yields in forcing culture of strawberry.
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