Overhead supplemental far-red light stimulates tomato growth under intra-canopy lighting with LEDs

Abstract

Far-red (FR) light regulates phytochrome-mediated morphological and physiological plant responses. This study aims to investigate how greenhouse tomato morphology and production response to different durations of FR light during daytime and at the end of day (EOD). High-wire tomato plants were grown under intra-canopy lighting consisting of red (peak wavelength at 640 nm) and blue (peak wavelength at 450 nm) light-emitting diodes (LEDs) with photosynthetic photon flux density (PPFD) of 144 μmol m-2 s-1 at 10 cm away from the lamps, and combined with overhead supplemental FR light (peak wavelength at 735 nm) with PPFD of 43 μmol m-2 s-1 at 20 cm below the lamps. Plants were exposed to three durations of FR supplemental lighting including: 06:00-18:00 (FR12), 18:00-19:30 (EOD-FR1.5), 18:00-18:30 (EOD-FR0.5), and control that without supplemental FR light. The results showed that supplemental FR light significantly stimulated stem elongation thereby resulting in longer plants compared with the control. Moreover, FR light altered leaf morphology toward higher leaf length/width ratio and larger leaf area. The altered plant architecture in FR supplemented plants led to a more homogeneous light distribution inside the canopy. Total plant biomass was increased by 9-16% under supplemental FR light in comparison with control, which led to 7-12% increase in ripe fruit yield. Soluble sugar content of the ripe tomato fruit was slightly decreased by longer exposure of the plants to FR light. Dry matter partitioning to different plant organs were not substantially affected by the FR light treatments. No significant differences were observed among the three FR light treatments in plant morphology as well as yield and biomass production. We conclude that under intra-canopy lighting, overhead supplemental FR light stimulates tomato growth and production. And supplementary of EOD-FR0.5 is more favorable, as it consumes less electricity but induces similar effects on plant morphology and yield.

Increasing Growth and Yield of Sweet Basil and Holy Basil by Application of Far-Red Radiation for Indoor Horticulture

“…This is in accordance to study of Park and Runkle (2017) on snapdragon and geranium under R:B with FR that could increase shoot dry weight by 28-50%. This is further confirmed by Zhang et al (2019) who provided the study results that the R:B LED (R 640 nm, B 450 nm) in combination with FR (735 nm) at 43 μmolm -2 sec -1 could increase the total plant biomass of high-wire tomato plants by 16% better than sole R:B LED (Zhang et al, 2019). Meng and Runkle (2017) reported that the B and R did not influence the biomass of basil.…”

“…The holy basil under R:B.3.5+FR50 increased the average leaf number by 295 and 64% of R:B.3.5 and R:B.7 and increased average leaf area by 89% of R:B.3.5 and 59% of R:B.7. FR light clearly indicated the leaf morphological development, FR light (735 nm) at 43 μmolm -2 sec -1 with R:B produce larger leaf area of tomato when compared to R:B without FR (Zhang et al, 2019). FR (700-800 nm) was an influence on the size of leaves, total leaf area of geranium and snapdragon by 7%.…”

“…This caused to increase the total fresh weight. Zhang et al (2019) reported that the R:B with FR increased total plant biomass of tomato. Moreover, FR increased the total biomass of basil by adding FR (30 μmolm -2 sec -1 ) to R:B light more than without FR (Meng and Runkle, 2017).…”

“…Although, the leaves area of the sweet basil under R:B.3.5+FR50 was not significantly different (p<0.05) from R:B.3.5 and R:B.7 but photosynthetic potential was increased because of the larger total leaves area of the plant (by many leaves number). The photosynthetic rate improved and would affect the promotion of the length of stem, extension growth and total plant biomass (Zhang et al, 2019;Park and Runkel, 2017;Heliospectra, 2019).…”

“…Many types/techniques of the LED horticultural light are Red (R)-Blue (B) LED, red-blue plus UV and Far-Red (FR), mixed-color (RGB) LED and white LED (Watjanatepin et al, 2018). The FR light regulates the phytochrome-mediated morphological and physiological plant responses and increases leaves and total biomass of the high-wire tomato (Zhang et al, 2019). In addition, the FR light also increases total leaves area and shoot dry weight of geranium and snapdragon (Park and Runkel, 2017).…”