2019 ASHS Annual Conference
Characterization of Solar Radiation Spectral Contribution in Lettuce Bolting and Flowering Using LEDs in an Indoor Setting
Characterization of Solar Radiation Spectral Contribution in Lettuce Bolting and Flowering Using LEDs in an Indoor Setting
Tuesday, July 23, 2019: 3:15 PM
Cohiba 1-3 (Tropicana Las Vegas)
Lettuce bolting, induced by heat stress, plant age, and photoperiod is a detrimental trait as it reduces crop marketability and limits production season in the field. However, the impact of light quality on bolting is not fully understood. On a previous study, we found a light quality treatment with similar blue (B), green (G), red, and far-red (Fr) spectral ratios than solar spectrum (28B:35G:37R with 1.2R/Fr) that triggered flowering (stem elongation and rosette formation) on lettuce grown indoors. The objective of this experiment is to characterize how the different sunlight spectral components B, G, R, and Fr contribute to bolting initiation. To examine the role of each color on bolting, four light treatments were used, described as percent photosynthetic photon flux (PPF) and R/Fr ratio (B:G:R-R/Fr): (1) 28B:35G:37R-1.2R/Fr, (2) 28B:35G:37R-126R/Fr, (3) 43B:0G:57R-1R/Fr, and (4) 43B:0G:57R-15R/Fr. From day 3-11 plants were provided with 75 µmol·m-2·s-1 PPF for 18 h and increased to 150 µmol·m-2·s-1 PPF for 18 h from day 12 to 68. Morphological data was collected on day 18, 25, 32, 39, and 68. On harvest day 68, differences in stem length, which measures initial bolting response, were found. Plants grown in 28B:35G:37R-1.2R/Fr had 30% longer stems than in 43B:0G:57R-1R/Fr. Plants in 28B:35G:37R-126R/Fr and 43B:0G:57R-15R/Fr had 4.8- and 5.3-times shorter stem length than in 28B:35G:37R-1.2R/Fr, respectively. Additionally, plants in 28B:35G:37R-1.2R/Fr and 43B:0G:57R-1R/Fr had 3.9-5.0 times greater stem fresh mass than in 43B:0G:57R-15R/Fr and 28B:35G:37R-126R/Fr. No differences were found in total fresh or dry mass but plants in 43B:0G:57R-15R/Fr and in 43B:0G:57R-1R/Fr had 36% and 31% greater leaf fresh mass than in 28B:35G:37R-1.2R/Fr. Leaf area in 43B:0G:57R-1R/Fr and in 28B:35G:37R-1.2R/Fr was 11% and 8% greater than 28B:35G:37R-126R/Fr, respectively. These results demonstrate how individual colors can both regulate and accelerate the physiological transition towards the lettuce reproductive stage.