Effect of light quality on growth of everbearing strawberry plants

The effects of various light sources for night irradiation on the growth of everbearing strawberry plants (Fragaria × ananassa Duch. 'Natsuakari') were investigated. The experiment was conducted in natural light-type phytotrons in which the day (6:00-18:00)/night (18:00-6:00) temperatures were controlled to 25/20°C. Plants were grown under natural daylight from 9:00 to 17:00, and were covered with a double silver polyethylene film from 17:00 to the following 9:00. Except in the case of plants receiving the 8-h photoperiod treatment (8-h), supplemental light was provided with white incandescent lamps (W), red fluorescent lamps (R), or far-red fluorescent lamps (FR) from 17:00 to 9:00. The experiment was carried out for 16 weeks, from 7 July 2006 to 26 October 2006. During the test period, leaves expanded continuously under all treatments, but more leaves expanded under the R light than under the 8-h, W, or FR light. In contrast, the number of inflorescences per plant was highest under the FR light, followed by the W, R, and 8-h light. Under the R light, the number of inflorescences was almost the same as that of under the 8-h light. These results indicated that inflorescence production of everbearing strawberry plants is promoted by FR light and leaf production is promoted by R light.