Plant shape, and thereby plant architecture, is a major component of the visual quality of ornamental plants. Plant architecture results from growth and branching processes and is dependent on genetic and environmental factors such as light quality.
The effects of genotype and light quality and their interaction were evaluated on rose bush architecture. In a climatic growth chamber, three cultivars (Baipome, Knock Out Radrazz and ‘The Fairy’) with contrasting architecture were exposed to three different light spectra, using white (W), red (R), and far-red (FR) light-emitting diodes (LEDs), i.e., W, WR, and WRFR. The R/FR ratio varied between treatments, ranging from 7.5 for WRFR to 23.2 for WR.
Light intensity (224.6 μmol m−2 s−1) was the same for all treatments. Plants were grown up to the order 1 axis flowering stage, and their architecture was digitized at two observation scales—plant and axis. Highly significant genotype and light quality effects were revealed for most of the variables measured. An increase in stem length, in the number of axes and in the number of flowered axes was observed under the FR enriched light, WRFR. However, a strong genotype × light quality interaction, i.e., a genotype-specific response was highlighted.
More in-depth eco-physiological and biochemical investigations are needed to better understand rose behavior in response to light quality and thus identify the determinants of the genotype × light quality interaction.