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  Eur.J.Hortic.Sci. 85 (5) 339-343 | DOI: 10.17660/eJHS.2020/85.5.5
ISSN 1611-4426 print and 1611-4434 online | © ISHS 2020 | European Journal of Horticultural Science | Original article

Spectral manipulations to elicit desired quality attributes of herbaceous specialty crops

N. Kelly and E.S. Runkle
Department of Horticulture, Michigan State University, East Lansing, Michigan, USA

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.

Keywords floriculture transplants, indoor farming, leafy greens, light-emitting diodes, light quality, photomorphogenesis, pigmentation

Significance of this study

What is already known on this subject?

  • This paper outlines what is known about the effects of the radiation spectrum on plant quality attributes when crops are grown indoors under sole-source lighting. It discusses how radiation wavebands can be manipulated to elicit certain desirable traits that are important for both growers and consumers.
What are the new findings?
  • This paper does not present any new research, but instead provides a synthesis of relevant research on the effects of radiation quality on high-value specialty crops such as leafy greens and herbaceous ornamental crops. Furthermore, this paper provides information on how radiation wavebands interact to affect multiple plant quality attributes.
What is the expected impact on horticulture?
  • The objective of this paper is to inform researchers and lighting professionals of recent advances in the area of plant quality manipulations through changes in the indoor lighting environment. It also provides indoor farmers with an easily digestible compilation of research about how the lighting environment regulates plant growth and quality attributes.

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Received: 31 October 2019 | Accepted: 6 April 2020 | Published: 21 October 2020 | Available online: 21 October 2020

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