Effects of Continuous Lighting and Time of Initiation of Treatments on the Flowering Time and Growth of Everbearing Strawberry Nursery Plants in a Closed Plant Factory

Abstract

To reduce initial costs and shorten the cultivation period (to reduce running costs) of the cultivation of strawberries in a closed plant factory we investigated the effects of light period and time of initiation of treatments on the flowering and growth of the everbearing strawberry (Fragaria×ananassa Duch. 'HS138') nursery plants. We used blue fluorescent lamps as the light source under 13 mol m-2 d-1 of daily light integral (DLI) in all treatments. Three treatments were performed as follows: 16-h light period (B16) and continuous lighting (B24) from 21 days after the transplanting of nursery plants from a micropropagation system to a hydroponic culture system and continuous lighting treatment from 5 days after transplanting (the time of initiation of continuous lighting treatment was 16 days earlier than that of the B24 treatment [EB24]). The experiment was terminated when all the plants under the treatments showed flowering (71 days after the initiation of the light period treatments). The plants in both B24 and EB24 treatments flowered about 20 days earlier than those in the B16 treatment. The leaf area per plant at the initiation of the light period treatment in B24 (21 days after transplanting) and EB24 (5 days after transplanting) was about 50 and 10 cm 2 respectively. These results indicated that one of the reasons why the EB24 treatment did not promote flowering was probably because of insufficient plant growth (leaf area) and age required for the transition from juvenile phase to reproductive phase. The total dry weight at the end of the experiment did not differ significantly between the B16 and B24 treatments. No physiological disorder was observed in the plants grown under continuous lighting. If plants can grow under the same DLI condition then continuous lighting can reduce the initial cost of a lighting system in the closed plant factory to two-thirds of the cost for the 16-h light period. Therefore cultivation of the everbearing strawberry under continuous lighting can reduce not only the running cost but also the initial cost in comparison with the cultivation of the everbearing strawberry under a 16-h light period. 21