Supplemental lighting techniques in greenhouses can increase plant growth and yield but require substantial amounts of energy. We proposed the use of energy-saving supplemental lighting, which was applied during rapid fruit development when the transport of photosynthetic products into the fruit was active. We measured the physiological responses (photosynthesis, growth, yield) of the strawberry plants with single fruit truss, wherein the following 3 treatments were made: plants were cultivated with no supplemental lighting (control), supplemental lighting throughout the experimental period (normal-light), and supplemental lighting during rapid fruit development (short-light). The period of rapid fruit development corresponded to 33% of the experimental period, and the cumulative light intensity for the short-light treatment was half of that for the normal-light treatment, and twice that of the control treatment. Consequently, the leaf area and dry weight of the plant body were significantly increased following normal-light and short-light treatments compared with the control treatment. The yield for the short-light treatment was also increased and nearly equal to that of the normal-light treatment but no significance to the control treatment. However, the energy use efficiency of the short-light was improved 1.5-fold compared to the normal-light treatment. Thus, shortening the period of supplemental lighting in accordance with the characteristics of fruit development is potentially effective.
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