End-of-production Supplemental Lighting with Red and Blue Light-emitting Diodes (LEDs) Influences Red Pigmentation of Four Lettuce Varieties

Abstract

<jats:p>Under low-light greenhouse conditions, such as those found in northern latitudes, foliage of red leaf lettuce (<jats:italic>Lactuca sativa</jats:italic> L.) varieties is often green and not visually appealing to consumers. Our objective was to quantify the effect of end-of-production (EOP; prior to harvest) supplemental lighting (SL) of different sources and intensities on foliage color of four red leaf lettuce varieties, ‘Cherokee’, ‘Magenta’, ‘Ruby Sky’, and ‘Vulcan’. Plants were finished under greenhouse ambient solar light and provided with 16-hours of day-extension lighting from low intensity light-emitting diode (LED) lamps [7:11:33:49 blue:green:red:far red (control)] delivering 4.5 μmol·m<jats:sup>−2</jats:sup>·s<jats:sup>−1</jats:sup>, or 16-hours of EOP SL from high-pressure sodium (HPS) lamps delivering 70 μmol·m<jats:sup>−2</jats:sup>·s<jats:sup>−1</jats:sup>, or LED arrays [100:0, 0:100, or 50:50 (%) red:blue] delivering 100 μmol·m<jats:sup>−2</jats:sup>·s<jats:sup>−1</jats:sup>, or 0:100 blue LEDs delivering 25 or 50 μmol·m<jats:sup>−2</jats:sup>·s<jats:sup>−1</jats:sup>. Relative chlorophyll content (RCC) and foliage L* (lightness), and chromametric a* (change from green to red) and b* (change from yellow to blue) values were significantly influenced by EOP SL and days of exposure. Generally, RCC of all varieties increased from day 3 to 14 when provided with EOP SL from the HPS lamps and LEDs delivering 100 μmol·m<jats:sup>−2</jats:sup>·s<jats:sup>−1</jats:sup>. End-of-production SL providing 100 μmol·m<jats:sup>−2</jats:sup>·s<jats:sup>−1</jats:sup> of 100:0, 0:100, or 50:50 red:blue light for ≥5 days resulted in increasing a* (red) and decreasing L* (darker foliage), b* (blue), and <jats:italic>h</jats:italic>° (hue angle; a measure of tone) for all varieties. Our data suggests that a minimum of 5 days of EOP SL providing 100 μmol·m<jats:sup>−2</jats:sup>·s<jats:sup>−1</jats:sup> of 100:0, 0:100, or 50:50 red:blue light enhanced red pigmentation of ‘Cherokee’, ‘Magenta’, ‘Ruby Sky’, and ‘Vulcan’ leaves when plants are grown under a low greenhouse daily light integrals (DLIs) &lt;10 mol·m<jats:sup>−2</jats:sup>·d<jats:sup>−1</jats:sup>.</jats:p>

Geranium and Purple Fountain Grass Leaf Pigmentation Is Influenced by End-of-Production Supplemental Lighting with Red and Blue Light-emitting Diodes

“…Compared with no EOP SL (control), RCC of geranium was significantly higher under LED EOP SL delivering 100 mmol · m -2 · s -1 . Similarly, Owen and Lopez (2015) reported 14 d of EOP SL delivering 100 mmol · m -2 · s -1 provided by 100:0, 0:100, or 50:50 red:blue light, resulted in increased RCC from 29.6 to 32.8 and 26.5 to 29.0 for lettuce 'Cherokee' and 'Ruby Sky' plants, respectively, compared with the control.…”

“…For fountain grass, regardless of EOP SL source, RCC significantly increased up to 14 d after exposure to EOP SL; however, an additional 7 d (21 d) of exposure to EOP SL resulted in no significant differences ( respectively, when fountain grass was finished under 70 mmol · m -2 · s -1 delivered from a HPS lamp. Owen and Lopez (2015) also reported that an additional 2 d (from 5 to 7 d) of 50:50 red:blue EOP SL delivering 100 mmol · m -2 · s -1 did not significantly influence RCC of lettuce 'Vulcan' plants. However, in the present study, increasing proportions of blue light significantly increased RCC.…”

“…The intensity and distribution of chlorophylls and anthocyanins are known to contribute to leaf color (Gazula et al, 2007). Environmental factors such as light quantity, quality, and duration and temperature can strongly influence the accumulation of these pigments (Owen and Lopez, 2015). In the present study, it was determined that the RCC of geranium was greatest when plants were finished under 14 d of EOP SL provided by HPS lamp delivering 70 mmol · m -2 · s -1 , 100:0, 87:13, or 50:50 red:blue light delivering 100 mmol · m -2 · s -1 , or 0:100 red:blue light delivering 25 or 100 mmol · m -2 · s -1 .…”

“…However, little is known regarding the short-term use of LEDs to enhance foliage color and the aesthetic quality of floriculture crops. Recently, Owen and Lopez (2015) found 5 to 7 d of EOP (before harvest) SL from LEDs providing 100 mmol · m -2 · s -1 of 100:0, 50:50, or 0:100 red:blue light for 16-h increased foliage color of four varieties of red leaf lettuce (Lactuca sativa L. 'Cherokee', 'Magenta', 'Ruby Sky', and 'Vulcan'). Therefore, shortterm exposure of monochromatic or combinations of narrow spectrum SL from LEDs is a potential lighting application for bedding plant producers to enhance aesthetic qualities such as leaf color.…”

Minimum Light Requirements for Indoor Gardening of Lettuce

“…2, 3). Furthermore, red pigmentation of lettuce leaves is a key component that influences consumer perception of product quality, as it is typically associated with higher anthocyanin content in the foliage (Gazula et al, 2007; Owen and Lopez, 2015; Ryder, 1999). When comparing results for the lowest and highest DLI evaluated in our study, anthocyanin content increased with increasing DLI by 4100% in Experiment 2, and by 1525% in Experiment 3.…”