The Effects of End-of-the-day Red and Far-red Light on Growth and Flowering of Petunia ×hybrida `Countdown Burgundy' Grown under Photoselective Films

Abstract

The objective of this research was to investigate if brief exposure to end-of-the-day (EOD) red (R) or far red (FR) light can overcome the flowering delay of petunia (Petunia ×hybrida Vilm.-Andr. `Countdown Burgundy') grown under FR deficient greenhouse environments with no adverse effects on stem elongation. Plants were grown under clear, FR, and R light absorbing greenhouse films (control, AFR, and AR films, respectively) and exposed to R or FR light at the end of the photoperiod for 15 minutes. At flowering, main stem of plants grown under the AR film was about 17% longer and that of AFR film grown plants (without EOD treatment) was about 50% shorter than control plants. EOD-R light reduced stem elongation of control plants but had no effect on AFR or AR film-grown plants. EOD-FR light increased stem elongation in plants grown under AR and AFR films but the percentage increase was greater under AFR film (7%, 19%, and 64% increase in control, AR, and AFR films, respectively). However, plants that received EOD-FR light under AFR film were 25% shorter than control plants that received no EOD light. AFR film delayed flowering by 11 days but AR film had no effect. Fifteen-minute exposure to EOD-R or -FR light had no effect on flowering under control and AFR film. Although the exposure to brief EOD-FR partially increased stem elongation, it was not sufficient to accelerate flowering. Treatments to enhance flowering can cause stem elongation. Therefore, care should be taken to avoid improper crop timing, especially with long-day plants.