Elongation responses of tomato (Solanum lycopersicum) seedlings to mimicked natural light and morning red light pulse under different DIF

MSc-thesis abstract (submitted 9 March 2018): Controlling plant height using a non-chemical method is one of the goals in protected horticulture production. Difference between day and night temperature (DIF) and changes in spectral quality at specific part of the photoperiod are two environmental factors studied extensively as potential growth regulators. However, most of the insights on how these environmental factors influence growth were obtained from experiments conducted at laboratory condition where light intensity and spectral distribution are usually constant during the diurnal cycle (constant light). It is not clear how plant growth changes if plants grow in a more realistic condition where light intensity and quality change during the 24-hour cycle of a day.

Therefore, to provide insights what might change in plant growth in a more realistic condition, a series of experiments were conducted in growth cabinets filled with lamps which produce intensity and spectrum similar to that of natural outdoor daylight (mimicked natural light). Moreover, the effects of morning red light pulse (one hour) on plant growth in mimicked natural light was studied.
All experiments were conducted in tomato (Solanum lycopersicum cv. ‘Money maker’) seedlings grown at either positive or negative DIF (10°C) in combination with different lighting conditions.

The result indicates seedlings grow longer (11% and 24% longer hypocotyl, 32% and 60% longer epicotyl respectively at positive and negative DIF) in mimicked natural light compared to constant light.
These increases were due to variable light quality instead of variable light intensity.

In the experiment on morning red light pulse, hypocotyl and epicotyl length were not influenced by additional morning red light under both DIF conditions. Only leaf area decreased by morning red light pulse.

Our results show growth under constant light intensity and quality underestimate plant growth compared to growth under mimicked natural light (variable light intensity and quality).
Moreover, morning red light pulse is not effective in reducing plant elongation growth.

Key words: mimicked natural light; constant light; morning red light pulse; seedling elongation; DIF