The effect of adding far-red light to white or red/blue supplemental LED lighting on growth and development of two tomato cultivars under greenhouse conditions

MSc-thesis abstract (submitted 4 May 2017): Far-red regulates various photobiological processes in plants by converting active form (Pfr) into inactive form (Pr) of phytochromes.
A greenhouse experiment was conducted to elucidate the effect of additional far-red to white or red/blue supplemental light-emitting diode (LED) background on growth and development of two tomato cultivars (Moneymaker and Foundation).
The role of phytochrome stationary state (PSS) value, determined by the proportion of total phytochrome in its active form (Pfr) was evaluated.
Important traits analysed were stem and leaf development, plant height, leaf area, specific leaf area, light interception, light use efficiency, total chlorophyll and carotenoid content, leaf absorbance, flowering time, photosynthesis, total biomass, and fruit yield.

Tomato seedlings (transplanted when reached two true leaves) were grown in greenhouse with experiment conducted in a split-plot design with five light treatments (white, white+30 µmol m-2 s-1 far-red, red/blue, red/blue+30 µmol m-2 s-1, and red/blue+50 µmol m-2 s-1). The supplemental light at plant height was at the level of 150 µmol m-2 s-1 PAR in all treatments, and natural light was included during growth period (81 days) starting from mid December 2016.

Plant height, light interception, fruit number, and fruit yield increased proportionally to increasing far-red intensity and decreased to increasing PSS value.
Flowering time of the second and third trusses was accelerated by far-red light, irrespective of the red/blue or white supplemental LED background.
Leaf appearance rate and stem elongation rate were higher when far-red was added, but not between far-red light treatments.
Additional far-red did not affect total chlorophyll and carotenoid content, total biomass, leaf area, and photosynthesis.
The same PSS value resulted in a similar stem elongation rate and leaf area, (partially contributed to light interception), total biomass and fruit yield; moreover, the effect of PSS was cultivar and trait dependent.

The importance of far-red light in regulating morphological and photobiological processes was recorded; nevertheless, how much far-red and/or for how long should that be applied needs to be further investigated for commercial production because growers have to take into account the extra cost for far-red lamps, as well as additional electricity consumption.

Finally, it is worth noting that these practices affect the prioritisation between vegetative growth and generative development to optimize crop production since stem and fruit increases were directed from the leaf expense.

Key words: Far-red ; growth and development ; phytochromes ; phytochrome stationary state ; PSS ; tomato cultivars ; white and red/blue LED lighting