S08 - Session O1 - Controlling photoperiodic flowering of shortday plants using a dynamic light spectrum

Authors: Malleshaiah SharathKumar *, Leo F M Marcelis , Ep Heuvelink

Sole-source LED lighting enables spectral flexibility to achieve desirable plant characteristics and product quality. An earlier study from our lab showed that short-day plant chrysanthemum flowers normally under long days of 11h dichromatic red-blue light extended with 4h sole blue LED light. Such dynamic LED lighting is possible in vertical farms and opens the possibility for shortday plants to provide a higher daily light integral by providing more hours of light (blue extended long days) without compromising flowering. However, whether this dynamic light spectrum would also result in normal flowering for other short-day species is still unknown. This study aims to investigate for several short-day species whether normal flowering is obtained when 11h of red-blue is extended with 4h of sole blue LED light. Nine short-day plant species were grown at three light regimes: 11h red-blue short-day (RB,SD), 15h red-blue long-day (RB,LD), and 11h red-blue plus 4h blue light long-day (RB+B,LD). Mixed red and blue light (ratio 60:40) was provided at a total PPFD of 100 +- 10 µmol m -2 s -1 and sole blue light was provided at 40 +- 5 µmol m -2 s -1 PPFD (Photosynthetic Photon Flux Density). Kalanchoe, Perilla and Stevia flowered only in RB,SD and not in long-day treatments (RB+B,LD and RB,LD). Artemisia, Chrysanthemum ( C. seticuspe and C. morifolium ), Cosmos, Poinsettia and Wild tomato ( Solanum habrochaites ) species flowered under RB,SD and RB+B,LD but not in RB,LD. This study shows that the photoperiodic flowering under a dynamic light spectrum is species dependent. Several short-day species showed normal flowering under blue extended long-days, but this response is not universal for all short-day plants. Such dynamic LED lighting will be helpful to develop species-specific light management programs in vertical farms and opens the possibility to produce short-day plants under blue extended long-days without compromising flowering.