Continuous Light Does Not Compromise Growth and Yield in Mini-Cucumber Greenhouse Production with Supplemental LED Light

Abstract

Continuous lighting (CL, 24h) can reduce the light intensity/light capital costs used to achieve the desired amount of light for year-round greenhouse vegetable production in comparison to short photoperiods of lighting. However, growth under CL has led to leaf injury characterized by chlorosis unless a thermoperiod or alternating light spectrum during CL is used. To date, there is no literature relating to how cucumbers (Cucumis sativus) respond to CL with LEDs in a full production cycle. Here, we evaluated a mini-cucumber cv. “Bonwell” grown under 4 supplemental lighting strategies: Treatment 1 (T1, the control) was 16 h of combined red light and blue light followed by 8 h of darkness. Treatment 2 (T2) had continuous (24 h) red light and blue light. Treatment 3 (T3) was 16 h of red light followed by 8 h of blue light. Treatment 4 (T4) was 12 h of red light followed by 12 h of blue light. All treatments had a supplemental daily light integral (DLI) of ~10 mol m−2 d−1. Plants from all treatments showed similar growth characteristics throughout the production cycle. However, plants grown under all three CL treatments had higher chlorophyll concentrations from leaves at the top of the canopy when compared to T1. The overall photosynthetic capacity, light use efficiency, and photosynthetic parameters related to light response curves (i.e., dark respiration, light compensation point, quantum yield, and photosynthetic maximum), as well as the quantum yield of photosystem II (PSII; Fv/Fm) were similar among the treatments. Plants grown under all CL treatments produced a similar yield compared to the control treatment (T1). These results indicate that mini-cucumber cv. “Bonwell” is tolerant to CL, and CL is a viable and economical lighting strategy for mini-cucumber production.

The Power of Far-Red Light at Night: Photomorphogenic, Physiological, and Yield Response in Pepper During Dynamic 24 Hour Lighting

“…In contrast to our current study, the use of monochromatic blue light at 100 μmol m –2 s –1 ( Velez-Ramirez et al, 2017 ) or 150 μmol m –2 s –1 ( Matsuda et al, 2016 ) during the night produced a high degree of injury in tomatoes. However, our previous studies on tomato ( Lanoue et al, 2019 ) and cucumber ( Lanoue et al, 2021b ) differ from this trend and indicate that the use of low intensity monochromatic blue light (50 μmol m –2 s –1 ) during the night was able to avert injury. In this study, nighttime blue light was considerably higher than the light compensation point ( Table 2 ), and between that used in Velez-Ramirez et al (2017) and Lanoue et al (2019) , and drove appreciable amounts of photosynthesis in 16W + 8B and 16W + 8BFR during the night ( Figure 3B ) without causing injury ( Figures 4 , 5 ).…”

“…Therefore, the feasibility of CL strategies hinges on whether the production (yield and quality) is equal to or greater than the conventional 16 h photoperiod lighting (control, 16W in this study). Due to their unique attributes, LEDs allow for the use of a dynamic CL strategy which employs a reduction in light intensity and/or change in spectral composition between day and night periods, which has been shown to eliminate or reduce injury in lettuce ( Ohtake et al, 2018 ), tomato ( Matsuda et al, 2016 ; Lanoue et al, 2019 ; Pham and Chun, 2020 ), and cucumber ( Lanoue et al, 2021b ). In this study with peppers, we showed that plants grown under two dynamic CL strategies (16W + 8B and 16W + 8BFR) were able to avert injury and maintain fruit yield and size (grade) when compared to the 16h control (16W; Figures 3 , 5 , 7 ).…”

“…In this study, 16W + 8BFR can reduce the intensity or installed capacity of light fixtures by 19% ( Table 1 ). A dynamic CL using a smart 24 h LED system can reduce light intensity/fixture capacity by a third and is more cost-effective than a conventional 16 h LED system in mini-cucumber production based on the cost of electricity per unit of produce, in Ontario ( Lanoue et al, 2021b ). The benefit of the reduction in light intensity/fixture requirement with the dynamic low-intensity CL will not change regardless of the electrical prices during the day/night.…”

“…However, exceeding the tolerable limits of photoperiods, which are species-specific, can lead to diminished yield, photoperiod-related leaf injury, and an economic disadvantage for growers ( Demers and Gosselin, 2002 ; Hao et al, 2018a ). While lettuce ( Ohtake et al, 2018 ) and cucumber ( Lanoue et al, 2021b ) are more tolerant to extended photoperiods including 24 h continuous lighting (CL), others such as tomato ( Velez-Ramirez et al, 2014 ; Matsuda et al, 2016 ) and pepper ( Demers and Gosselin, 2002 ) are susceptible to photoperiod related injury. Photoperiod injury can manifest in many ways including interveinal chlorosis which leads to lower photosynthetic rates and ultimately reductions in yield ( Sysoeva et al, 2010 ; Velez-Ramirez et al, 2011 ).…”

Light Spectra and Root Stocks Affect Response of Greenhouse Tomatoes to Long Photoperiod of Supplemental Lighting

“…However, if photoperiod-related injury can be avoided, an increase in plant growth and yield is theoretically possible [ 8 ]. The use of wavelength-specific LEDs has shown promise in reducing photoperiod-related injury during the vegetative growth stage [ 14 ]; however, little is known about how the use of wavelength-specific LEDs will affect the yield of high-wire-fruiting vegetables during extended photoperiods [ 7 , 40 ]. Between the months of February and April, those which followed the photoperiod-related injury in leaves, the average fruit weight (size, g fruit −1 ) was observed to decrease in both 23 h lighting treatments ( Figure 5 and Figure 8 ).…”