Light quality affects growth and nutrient content of basil

Basil is a culinary herb with large production and fresh market shares in the United States. A significant amount of the produced basil is grown in controlled environments with light emitting diodes (LEDs) as a sole lighting source. In this study, three cultivars of basil (‘Aroma 2’, ‘Dolly’ and ‘Nufar’) were evaluated. The light quality treatments included blue LEDs (peak emission at 450 nm), red LEDs (50:50, peaks at 625 and 660 nm), blue/red LEDs (20:40:40, peaks at 450, 625 and 660 nm), and white LEDs (5000 K). In addition, T5 fluorescent (4100 K) and natural greenhouse light supplemented with high-pressure sodium irradiance were used. The growing areas of LEDs and fluorescent were separated and shielded from natural and greenhouse light using an opaque blackout material. Plants were grown at a constant 21±2°C with a 16-h photoperiod at a photosynthetic photon flux density of approximately 150 µmol m^‑2 s^‑1. The plants were grown from seeding under the specific light qualities and the experiment was terminated after 50 days. Brix analysis was used to determine levels of soluble solids and sugar content in recently mature leaves. There was a trend for higher °Brix under blue LEDs among cultivars. The cultivar ‘Aroma 2’ had in general the greatest °Brix values to suggest higher sugar content than in leaves of ‘Dolly’ or ‘Nufar’. °Brix values above 4.0 were in general recorded for ‘Aroma 2’ except in the white LED environment. The blue/red environment supported growth and top dry weight well for ‘Aroma 2’ and ‘Nufar’. Least dry weight was observed for all cultivars under fluorescent irradiance. ‘Dolly’ appeared to be less suitable for control environment production compared to ‘Aroma 2’ or ‘Nufar’ based on dry weight accumulation. Soluble solids were also appreciably lower for ‘Dolly’ with the exception of the blue LED environment.