Spectral manipulations to elicit desired quality attributes of herbaceous specialty crops

Light-emitting diode (LED) technology has greatly advanced the practicality of growing high-value specialty crops in an indoor environment. Different lighting spectra can affect plant quality attributes of leafy greens (e.g., lettuce) such as leaf shape, texture, taste, coloration, and nutritional compounds. For instance, UV-A (315-400 nm) and blue (B; 400-500 nm) radiation can be used to increase anthocyanin concentrations, which are red-colored pigments that can accumulate in leaf tissue. Anthocyanins are part of a larger group of molecules (phenolics) that have nutritional value but can come at the expense of taste. For example, sensory studies of lettuce have demonstrated that plants with higher phenolic concentrations often have a more bitter taste and are therefore less appealing to consumers. Adding far-red (FR; 700-800 nm) radiation to a spectrum can increase leaf area and yield of lettuce but also decrease leaf coloration, thickness, and desired chemical concentrations. The quality characteristics desired for ornamental seedlings are somewhat different and can include compact growth and early or late flowering. Seedlings are highly responsive to the red (R; 600-700 nm) to FR ratio as well as photon flux density of B radiation. These can be manipulated to inhibit or promote extension growth and flowering. For example, decreasing the R:FR can accelerate flowering in some long-day plants, but not affect flowering in other cultivars and/or species. There are often trade-offs between some quality attributes and plant growth, which must be carefully considered when choosing an indoor lighting spectrum. Here, we summarize research-based findings as they relate to the effects of spectral manipulations on plant quality attributes.