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ISHS Acta Horticulturae 1134: VIII International Symposium on Light in Horticulture

In search of an optimized supplemental lighting spectrum for greenhouse tomato production with intracanopy lighting

Authors:   C. Gómez, C.A. Mitchell
Keywords:   far-red, high-wire tomato, LEDs, light quality, photon flux
DOI:   10.17660/ActaHortic.2016.1134.8
With anticipated energy-efficiency improvements and ever-improving light-distribution architectures, light-emitting diodes (LEDs) are a promising alternative to current supplemental lighting (SL) technologies for greenhouse crop production. Yet, significant questions remain regarding how to best optimize spectral-quality effects on plant growth and development using LEDs in the greenhouse. The objective of this study was to compare different spectra of intracanopy (IC) SL using LEDs for high-wire greenhouse tomato (Solanum lycopersicum 'Merlice') production in a mid-northern climate during a winter-to-summer production cycle. Five lighting treatments were evaluated: solar light only (control); solar light + SL from IC-LED towers using different percentages of blue, red and/or far-red light: 10B-90R; 30B-70R; 25B-60R-15FR; or 80R-20FR, where B refers to blue (450 nm), R refers to red (627 nm), and FR refers to far-red (730 nm). A constant photon flux of 180 µmol m-2 s-1 was provided to all plants grown with SL for 16 h d-1. In general, light quality from SL did not affect weekly plant-growth measurements (leaf length and stem elongation), relative chlorophyll content (RCC), or plant productivity (fruit number and total fruit FW), but significantly altered leaf photosynthesis and abaxial stomatal density (SD) and index (SI). Although leaves grown with 25B-60R-15FR had higher stomatal conductance (gs) than all other treatments, their abaxial stomatal features were only ~87% those of leaves grown with 10B-90R. Leaf chlorophyll content was up to 11% higher for plants grown under any kind of SL compared to unsupplemented controls. Similarly, total fruit yield was higher for SL treatments relative to the control. The consequences and perspectives of using different light-quality treatments in the SL spectrum will be discussed.

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