Blue-light-promoted elongation and flowering are not artifacts from 24-h lighting: a comparison with red light in four bedding plant species

Our previous study on bedding plants indicates that under 24-h lighting, pure blue light, compared to red light, can promote elongation or flowering.
The objective of this study was to investigate whether the blue light promotion effects are independent of photoperiod.
The growth and morphology traits of petunia (Petunia × hybrida ‘Duvet Red’), calibrachoa (Calibrachoa × hybrida ‘Kabloom Deep Blue’), geranium (Pelargonium × hortorum ‘Pinto Premium Salmon’), and marigold (Tagetes erecta ‘Antigua Orange’) were compared under two light quality treatments: 1) R, pure red light (665 nm); and 2) B, pure blue light (440 nm) using continuous (24-h light/0-h dark) or periodic (16-h light/8-h dark) light-emitting diode lighting.
A photosynthetic photon flux density of approximately 100 μmol m^‑2 s^‑1 and an air temperature of approximately 22°C was used for the above treatments.
For either transplants or mature plants, regardless of photoperiod, B promoted elongation growth compared to R, as demonstrated by a greater daily stem elongation rate, main stem length, internode length, or petiole length, with varying sensitivity among species.
Also, after transplanting, the plants under B showed an earlier flowering time than those under R, regardless of photoperiod.
However, the magnitude of B promotion was greater under 24-h than 16-h lighting in many cases.
This suggests that the promoted elongation and flowering by blue light is not specifically from 24-h lighting, although the promotion degrees differ between photoperiods and among species.

International Symposium on Advanced Technologies and Management for Innovative Greenhouses: GreenSys2019

Y. Kong, D. Kamath, Y. Zheng

photoperiod, light quality, plant height, flowering time

https://doi.org/10.17660/ActaHortic.2020.1296.84