S06 - Session P7 - The effect of four different top light LED spectra on growth and development of greenhouse-grown `Merlice´ and `Brioso´ tomato cultivars

Authors: Theoharis Ouzounis *, David Hawley

We assessed the effectiveness of four different LED light spectra applied as supplemental top lighting. Light fixtures were mixtures of red and broad-spectrum white LEDs, resulting in different fractions of red (R), green (G) and blue (B): (1) Red/Blue, (2) Pink, (3) Broad White/Red, and (4) Broad White. All treatments received the same PPFD of ~250 μmol m -2 s -1 at 20 cm from the top of the full-grown canopy and a 16 h photoperiod. Two tomato (Solanum lycopersicum) cultivars, 'Merlice' and 'Brioso' were grown according to a highwire system at a planting density of 2.74 plants m -2 on stonewool from October to March in 3 Venlo greenhouse compartments (3 replications). Each compartment consisted of 4 plots, where the 4 light treatments where randomly allocated. We determined plant growth and development, yield and fruit quality. Stem length was not influenced by light spectra, although for 'Merlice' stem length showed a tendency to increase linearly with increase in fraction red light (or decreased fraction blue). Number of leaves and number of trusses was not significantly different between the 4 light spectra. 'Merlice' showed a significant linear decrease in yield and total plant dry weight with increasing fraction red. For 'Brioso' an optimum response was observed (highest yield) under the Pink treatment. Fraction of biomass partitioned to the fruits, specific leaf area and leaf area index was not affected by light spectrum. No big differences between light spectra in fruit dry matter content, Brix and pH were observed. Fruit quality was not influenced by light spectrum. Interestingly enough, 'Merlice' showed a trend for increasing yield from winter to spring under Broad White and 'Brioso' under Pink (photoacclimation with solar light from winter to spring). Yield was affected in a cultivar-dependent manner. Consequently, our experiment recommends suitable LED light regimes for greenhouse tomato growth.