Growth and morphology of vegetable seedlings under different blue and red photon flux ratios using lightemitting diodes as sole-source lighting

Vertical-farming (VF) can be more energy-efficient with light-emitting diodes (LEDs) with higher efficiencies than fluorescent lamps (FL). Plant responses to blue (B) and red (R) light are species-specific. The objective was to evaluate B:R photon flux (PF) ratios for the production of vegetable seedlings. Cucumber ('Cumlaude') and tomato ('Komeett') were grown under 100 μmol m^-2 s^-1 PPF, 18-h photoperiod, and 25°C temperature. B (455-nm peak) and R (661-nm peak) LEDs were used as the sole source lighting and the percentage B PF was varied at 0, 10, 30, 50, 75, and 100%. For cucumber, hypocotyl length decreased with increasing B up to 75B. Plants in 0B, 10B, and 100B showed 156, 65, and 297%, respectively, greater hypocotyl length than under FL. Dry mass and leaf area decreased with increasing B from 10B to 75B. Plants under FL had 34 and 73% greater dry mass than in 75B and 0B, respectively and 48, 30, 55 and 68% greater leaf area than in 0B, 30B, 50B and 75B, respectively. For tomato, hypocotyl length also decreased with increasing B up to 75B. Plants in 0B, 10B, 30B, 50B, and 100B showed 113, 82, 32, 29 and 90%, respectively, greater hypocotyl length than under FL. Dry mass and leaf area increased with increasing B up to 30-50B, and then decreased from 50B to 100B. Plants in 30B and 50B had 66 and 59%, respectively, greater dry mass than plants in FL. Tomatoes under FL had 71 and 62% greater leaf area than in 0B and 100B, respectively. For cucumber seedlings, the optimal percent was 10B, which, however, produced taller seedlings with less dry mass than those under FL. For tomato, the optimal percent was 30B-50B, which produced seedlings with comparable morphology and growth as those under FL.