Location: Application Technology Research
Title: End-of-production cooling alters foliage color, yield, and nutrition of lettuceAuthor
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BREWER, DEVIN - Michigan State University |
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WALTERS, KELLIE - University Of Tennessee |
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ARMSTRONG, SARAH - University Of Tennessee |
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Boldt, Jennifer |
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LOPEZ, ROBERTO - Michigan State University |
Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/3/2024 Publication Date: 11/1/2024 Citation: Brewer, D., Walters, K., Armstrong, S.P., Boldt, J.K., Lopez, R.G. 2024. End-of-production cooling alters foliage color, yield, and nutrition of lettuce. Journal of the American Society for Horticultural Science. 149(6):365-378. https://doi.org/10.21273/JASHS05438-24. DOI: https://doi.org/10.21273/JASHS05438-24 Interpretive Summary: Controlled environment agriculture allows growers to provide precise growing conditions for crops. Adjusting the growing conditions to increase crop growth should also consider impacts to crop quality, resource use, and economic profitability. Red leaf lettuce grown at higher temperatures grow faster, but they often lack the vibrant red color desired by consumers. Providing low temperatures just prior to harvest offers a strategy to increase red leaf color while not slowing down crop growth too much. Two days of low temperature prior to harvest increased red lettuce leaf color, elemental concentrations, and nutrient profiles, while minimally impacting total fresh weight. This information will help growers utilize controlled environments to produce high yields of red leaf lettuce with desired color and quality attributes, while efficiently managing resource use. Technical Abstract: Plants synthesize anthocyanins to counteract oxidative damage from environmental stressors such as chilling injury. In controlled environments (CE), temperature can be adjusted to increase anthocyanin concentration and thus improve foliage color of crops prior to harvest. Our objective was to quantify how end-of-production (EOP) cooling influences yield, growth, development, and quality parameters such as mineral nutrient, carotenoid, and anthocyanin concentrations, and foliage color of red leaf lettuce (Latuca sativa). Seeds of red leaf lettuce ‘Barlach’, ‘Rouxai’, and ‘Thurinus’ were sown in a growth chamber with a mean daily temperature (MDT) set point of 22 °C, carbon dioxide (CO2) concentration of 500 µmol·mol'1, and a photosynthetic photon flux density (PPFD) of 180 µmol·m'2·s'1 provided by light-emitting diodes (LEDs). After 11 d, seedlings were transplanted into deep flow hydroponic tanks in the same growth chamber with a CO2 concentration of 800 µmol·mol-1, day/night temperature set point of 28/21 °C (MDT of 26 °C) and under LEDs that provided a PPFD of 300 µmol·m'2·s'1 for 17 h·d-1. During the last 6-8 days of production, plants were either left in the same conditions or transferred to growth chambers with a constant MDT of either 8, 14, 20, or 26 °C. Additionally, spectrum was adjusted to a ratio (%) of 75:25 blue (400–500 nm):red (600–700 nm) (B:R) light and a PPFD of 150 µmol·m'2·s'1. EOP cooling negatively influenced shoot fresh mass (SFM) and dry mass of ‘Barlach’, ‘Rouxai’, and ‘Thurinus’. Compared to uncooled plants, the SFM and SDM in the 14 °C EOP cooling treatment were 27% and 17% (‘Barlach’), 25% and 20% (‘Rouxai’), and 51% and 52% (‘Thurinus’) smaller, respectively. The chromametric a* value of each cultivar increased, indicating a change from green to red, under all EOP cooling treatments. By day 2, a* of ‘Rouxai’ and ‘Thurinus’ at 14 °C increased from -1.7 to 0.06 and from -0.99 to 1.08, respectively. By day 6 of EOP treatment, a* of ‘Barlach’ under the EOP 14 °C treatment increased from -4.18 to -1.66, while the a* of uncooled plants decreased from -5.06 to -6.97. In addition, EOP cooling generally increased mineral nutrient concentration. Foliar concentrations of magnesium (Mg), manganese (Mn), and zinc (Zn) increased by 23, 20, and 21% in ‘Barlach’, and by 26, 21, and 13% in ‘Rouxai’ at 14 °C. Plants exposed to EOP cooling also had greater anthocyanin concentrations. At 14 °C ‘Barlach’, ‘Rouxai’, and ‘Thurinus’ possessed 62, 53, and 59% greater anthocyanin than the control. We observed the highest concentration of violaxanthin, ß-carotene, and total carotenoids in each cultivar at 14 °C and the lowest under the control treatment. Total water-soluble vitamin (WSV) concentration was not affected by EOP cooling. However, we observed altered concentrations among the WSV, such as increased vitamin B1, but the lowest concentration of vitamin B6 for each cultivar in control plants. Additionally, as temperature decreased the concentration of vitamin B9 increased for ‘Barlach’ and ‘Thurinus’. Vitamin C was 24%, 29%, and 37% greater in ‘Barlach’ and 34%, 29%, and 45% greater in ‘Thurinus’ control plants than plants exposed to 20, 14, or 8 °C, respectively. |