Photoperiod and light quality modulate flowering progression and ornamental traits in Dahlia pinnata ‘Cafe au Lait’

This study examined how photoperiod and light quality affect flowering progression and ornamental traits in Dahlia pinnata ‘Cafe au Lait’. Plants were exposed to seven photoperiods or six light-quality treatments, and growth, floral traits, soluble sugars and endogenous hormones were assessed. Flowering was assessed using one threshold observation per treatment and was not subjected to inferential statistical analysis. Longer photoperiods generally supported greater plant height and stem diameter, while 12–14 h light treatments showed higher values for several floral traits. Light-quality treatments included white light (W), red light (R), blue light (B) and mixed red:blue spectra. White light was associated with greater plant height, the 5R:1B treatment with greater stem diameter, and blue light alone with fewer ray florets. RNA sequencing (RNA-seq) of vegetative and reproductive shoot apices identified DpELF3 as a candidate gene. Quantitative real-time PCR (qRT-PCR) showed photoperiod-responsive expression of DpELF3 . These findings describe cultivar-specific responses to the tested light environments and provide a basis for further evaluation of light management and candidate genes in dahlia.