Effects of different supplemental light spectrum on growth and development of Solanum lycopersicum L. “Cappricia”.

MSc-thesis abstract submitted 30 May 2016): To investigate the effects of different light spectrum on growth and development of tomato plants, plants of Solanum lycopersicum L. “Cappricia” were transferred to a greenhouse 33 or 34 days after sowing and exposed to 7 supplemental light treatments (150 µmol m-2 s-1 at canopy level) in winter time with the background of natural light (30% of supplemental light in a daily integral) for eight weeks.

Treatments comprised:
(1) 95% red + 5% blue LED (RB5)
(2) RB5 + 16 h 162 µmol m-2 s-1 far-red light (RB5+FR)
(3) RB5 + 16 h 76 µmol m-2 s-1FR (RB5+1/2FR)
(4) 88% red + 12% blue LED (RB12)
(5) RB5 + 1 h UV-B (RB5+UV)
(6) LED with 100% of blue light (Blue)
(7) HPS lamps (HPS).
LEDs and HPS lamps were switched on for 16 hours.

HPS lamps resulted in higher leaf appearance rate and faster flower development compared to RB5 LED modules. Additional FR (RB5+FR and RB5+1/2FR) resulted in faster flower development.

In general, 100% of blue light was sub-optimal for development with fewer trusses at the end of the experiment, lower fruit set and appearance of blossom end rot (BER). Lower pollen viability was found under RB12 compared with RB5.

Additional FR and HPS resulted in more than 40% (FR) and 20% (HPS) in total dry weight (TDW) and also larger leaf area. No significant difference was found in the two FR treatments regarding to TDW.

A larger specific leaf area (SLA) and thinner stems were found under 100% blue light. In addition, 100% blue light (PSS=0.52) resulted in similar elongation effect with RB5+1/2FR (PSS=0.77).

Physiological disorders such as missing apex, split truss and inconsistent leaf number between two successive trusses appeared in LED and HPS treatments. Additional FR and 100% of blue light eliminated these disorders.

Little effect of additional UV was observed in this experiment due to the limitation of UV-B measurement.

Key words: Greenhouse, supplemental lighting, light emitting diodes (LEDs), high pressure sodium (HPS) lamps, Solanum lycopersicum, fruit set, pollen viability, physiological disorders, additional far-red (FR)