ISHS Acta Horticulturae 711: V International Symposium on Artificial Lighting in Horticulture
DEVELOPMENTAL AND PHYSIOLOGICAL RESPONSES OF TOMATO AND CUCUMBER TO ADDITIONAL BLUE LIGHT |
| Authors: | C. Ménard, M. Dorais, T. Hovi, A. Gosselin |
| Keywords: | LED, fluorescence, photosynthesis, photoperiod, supplemental lighting |
| Abstract:
In the last 15 years, extensive studies on supplemental lighting of greenhouse crops have been realized. HPS lamps are the most commonly used type of light source in greenhouse production, and PPF and photoperiod recommendations for different species have been proposed. While they have an appropriate light spectrum for photosynthesis and a high efficiency, HPS lamps are relatively poor in blue and far-red compared to the solar PPF radiation. Moreover, extended or continuous lighting provided by HPS lamps may lead to physiological disorders for some species such as tomato. It is well known that spectral quality influences plant growth and development. For example, high ratios of red to far-red can stimulate phytochrome response (stem elongation, flowering, stomatal conductance or plant anatomy), while blue light is important in the formation of Chl, chloroplast development, activation of the circadian rhythm of photosynthesis, enzyme synthesis, and photomorphogenesis. The primary objective of this study was to compare the developmental and physiological changes in tomato and cucumber plants grown under HPS with different levels of blue light, and to evaluate the use of blue LEDs for extended and inner canopy lighting. Tomato (Lycopersicon esculentum ‘Trust’) and cucumber (Cucumis sativus ‘Bodega’) plants were grown under HPS lamps with or without blue LEDs (455 nm) for 12 or 20-h photoperiods. Plant development and biomass, gas exchange measurements (ACO2, gs, Ci), light (A/Q) and CO2 (A/ci) response curves, and Chl a fluorescence parameters have been measured weekly (cucumber) or bimonthly (tomato). Results showed that adding blue light inside the canopy increased plant biomass and fruit yield but did not offset the negative effect of extended photoperiod. Inner canopy lighting with high level of blue light was useful for cucumber but not for tomato. | |
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