Light quality regulates plant architecture in different genotypes of Chrysanthemum morifolium Ramat.

Specific light spectra play an important role in plant photomorphogenic responses. Plants are sensitive to light ranging from UV (280-400 nm) to far-red light (700-800 nm). The shoot architecture or plant shape is an important quality trait in ornamental plants and can be altered under specific light spectra. The shade avoidance syndrome is a well-documented response of plants to canopy shading and low R:FR conditions, characterized by shoot elongation and inhibited branching. Treatments with LED light combinations to obtain different spectral compositions were tested on rooted cuttings of 3 chrysanthemum genotypes (a pot chrysanthemum, a cut flower and a disbud chrysanthemum genotype) to assess the effect on shoot architecture. Red light treatment generally showed increased bud outgrowth and increased average bud length while blue + far-red light treatment resulted in decreased bud outgrowth and bud length. Some effects were genotype dependent, such as plant height, which increased under blue + far-red light treatments compared to red light treatment, only for the pot chrysanthemum genotype. Treatment with blue + far-red light in 25 decapitated cuttings showed a strong elongation of the topmost axillary bud and inhibition of underlying buds for the pot chrysanthemum and cut flower genotypes. This effect also persisted in greenhouse conditions.