Adding Far-Red to Red, Blue Supplemental Light-Emitting Diode Interlighting Improved Sweet Pepper Yield but Attenuated Carotenoid Content

Abstract

Supplemental interlighting is commonly used in modern greenhouses to improve light deficiency, but the light spectrum affects fruit quality and color change. This study aimed to analyze the effect of interlighting with red, blue, and additional far-red light on the fruit qualities and carotenoid contents of red and yellow sweet peppers (Capsicum annuum L.). Three light treatments were applied: natural light (NL), NL with red + blue LED interlighting (71 μmol m–2 s–1) (RB), and RB with far-red light (55 μmol m–2 s–1) (RBFR). Ascorbic acid, free sugars, and individual carotenoid content were quantified with HPLC analysis. Fruits were sampled on 2020.11.14 (Group 1) and 2021.01.03 (Group 2) from the plants grown under average light intensities of 335.9 and 105.6 μmol m–2 s–1, respectively. In the overall period, total yields in RB and RBFR were 22 and 33% higher than those in NL in red fruits and 2 and 21% higher in yellow fruits, respectively. In both colored fruits, ascorbic acid, total soluble sugar, and carotenoid content were higher in RB and RBFR than NL. In Group 1, ascorbic acid and total soluble sugar were significantly different between RB and RBFR only in red fruits. In Group 2, ascorbic acids in red and yellow fruits were 9 and 3% higher in RBFR than RB but total soluble sugars were 4 and 2% lower, respectively. Carotenoid contents in red and yellow fruits were 3.0- and 2.1-fold higher in RB and 2.0- and 1.4-fold higher in RBFR than those in NL, respectively. In this study, interlighting had a significant impact on fruit quality in Group 2, mainly due to the increase in the ratio of interlighting to total light by seasonal changes. In particular, red and yellow fruit yields were 9% and 19% higher in RBFR than RB, but carotenoid contents were 26 to 9% lower, respectively. This result exhibited that additional far-red lighting has a trade-off relationship between fruit yield and carotenoid content. Thus, it is necessary to provide an adequate light spectrum according to a specific cultivation purpose, such as improving yield or accumulating plastids in fruits.

Fruit quality and volatile compounds of greenhouse sweet peppers as affected by the LED spectrum of supplementary interlighting

“…In this study, the fruit weight was reduced more in RB than in fruits grown in FR. The reduced fruit weight in sweet pepper was previously observed in RB LED interlighting 25 . Based on these results, RB alone may increase total photosynthates but does not lead to an increase in fruit weight.…”

“…However, since flavor has a strong subjective domain, studies on correlating sensory evaluation with fruit physicochemical changes are very challenging; thus, more research is needed in the future. In addition, dramatic changes in flavor and volatiles compared to NL support that the interlighting technique can efficiently change the fruit quality or flavor composition by direct irradiance to fruits 25 . Thus, it is necessary to adequately adjust the position of interlighting LEDs according to the purpose of cultivation, whether to enhance photosynthesis or to improve fruit quality.…”

“…In strawberries, NL, incandescent light, and RB LED‐grown fruits were examined, in which RB LED‐grown strawberries demonstrated higher sugar content 23,24 . With sweet peppers, several studies have reported that interlighting with RB or FR LEDs increases leaf photosynthesis, fruit quality, and the yield of sweet peppers 25‐28 . However, studies on flavor‐related quality attributes such as firmness, texture, and taste under different lighting treatments have been limited.…”

Effects of light spectrum on the morphophysiology and gene expression of lateral branching in Pepino (Solanum muricatum)

“…Red light inhibits hypocotyl elongation and increases hypocotyl diameter in soybeans (Wang C. et al, 2022). Photosynthesis determines crop yield and quality, depending on the concentration of Chl a, Chl b, and carotenoids, which directly affect photosynthetic capacity (Kim and Son, 2022). In the seedlings of Pepino (Solanum muricatum), red light inhibits plant height, leaf development, and photosynthetic characteristics, and the contents of Chl a, Chl b, and carotenoids increase with an increased ratio of red light but decrease considerably with an increased ratio of blue light (Di et al, 2021).…”

Dry mass input into fruits can be predicted by fine root morphology of pepper cultivars exposed to varied lighting spectra

“…Only when exposed to the red LED light will dry mass weighted proportion be higher than 40% in fruits of three cultivars. The promotion of dry mass allocated to fruits in pepper can be a trade-off that attenuated synthesizing photosynthetic pigments (Kim and Son, 2022). It is reasonable that relative higher energy output in red light does not require response to input dry mass for obtaining more photosynthesis.…”