The effects of led lighting on the commercial cultivation of Stevia rebaudiana / Narendren Rengasamy
Stevia rebaudiana is a perennial plant from the Asteraceae family, native to the highlands of Brazil and Paraguay. It is a high-value crop due to the strong commercial demand for its metabolites (steviol glycosides, SG) as an organic low-caloric sweetener with up to 300 times the sweetness of con...
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| Format: | Thesis |
| Published: |
2023
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| Online Access: | http://studentsrepo.um.edu.my/15594/1/Narendren.pdf http://studentsrepo.um.edu.my/15594/2/Narendren_Rengasamy.pdf http://studentsrepo.um.edu.my/15594/ |
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| Summary: | Stevia rebaudiana is a perennial plant from the Asteraceae family, native to the highlands
of Brazil and Paraguay. It is a high-value crop due to the strong commercial demand for
its metabolites (steviol glycosides, SG) as an organic low-caloric sweetener with up to
300 times the sweetness of conventional sugar. Stevia rebaudiana a short-day plant, has
a tendency for a shortened vegetative stage and early flowering when grown under a
photoperiod of 12 h or less. The amount of SG in the leaves reduces by up to 50% after
flowering. Given the strong commercial demand for Stevia products, and the limited
supply available domestically, intense cultivation in controlled environment agriculture
(CEA) systems is a viable option. Lighting energy can account for more than 70% of the
total electrical energy used in a CEA system while the CEA system itself can consume
up to 100% more electrical energy compared to a conventional greenhouse. This study
included three experimental set-ups, using four different lighting strategies. All artificial
lighting systems used high powered light emitting diodes (LED). In the first experiment,
the plants were grown under Red + Blue light with photoperiods of 8, 12 or 16 hours (8H,
12H, 16H) and an intermittent photoperiod of 5 hours 20 minutes (16HI) per 8 hours (for
a total of 16 hours each day). A control sample was grown under natural sunlight and
photoperiod (12 hours) in the climate-controlled greenhouse (GH). In the second
experiment, the plants were grown under 6 different spectral compositions that had a base
Red + Blue (RB) spectra. The control plants were grown under pure RB spectra while
others were grown under RB supplemented with Far Red (FR), Ultraviolet A (UVA),
Blue (BR), Green (GR), FR+UVA+GR (FS). In the third experiment, varying fractions
of UV-A and green light in addition to the base RB was used. Two treatments with green
fractions (GR1 & GR2), two treatments with UVA (UV1 & UV2) and two treatments that
had both (UVGR1, UVGR2). A separate set of plants were grown under RB and natural
sunlight before being transferred to GR2, UV2, UVGR2, and monochromatic light treatments of blue, green and UVA, for 3 and 10 days before harvest. Plants grown under
the UVGR1 had the highest dry leaf biomass accumulation of 4.75 g plant-1 (P<.05).
UVA had the highest metabolite (ST + Reb A) concentration of 27% (P<.05) while plants
grown under sunlight had a mean SG concentration of 15%. UVGR1 had the highest
metabolite yields and energy use efficacy of 1.05 g plant-1 and 30.24 mg kWh-1 (P<.05)
respectively. In terms of productivity, the GR1 spectral composition was the most
productive, producing 18.7 (P<.05) milligrams of ST + Reb A compounds for every mol
of light used. Overall, this study demonstrated the effects of different lighting strategies
on the productivity and energy use efficacy of indoor grown Stevia rebaudiana. It was
observed that strategies that used spectral composition with green and UV-A were more
productive and had higher efficacies compared to photoperiod manipulation, or the use
of pre-harvest lighting.
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