Effects of different light types on root formation of Ocimum basilicum L. cuttings

• Blue light is effective at improving root formation of sweet basil.
• Establishment of basil cuttings is 3 times faster in blue light than natural light.
• Longer exposure to blue light resulted in leaf etiolation of older leaves.

Sweet basil is usually propagated by cuttings due to the ease of this method and the ability to establish mature plants quickly. However, slow root formation in this method limits early stage plant growth. To improve the efficiency of root formation, we evaluated the effects of different types of light on sweet basil cuttings. Basil cuttings were initially separated into NAA or non-NAA treatment groups to evaluate hormonal effects on rooting. Then, basil cuttings were irradiated with red, blue, fluorescent light, or natural sunlight for 16 h per day. Adventitious root and shoot fresh weights as well as chlorophyll content were measured at 2, 4, and 6 weeks. Blue light was the most effective at improving root formation. Root establishment was about three times faster upon treatment with blue light than natural sunlight; root growth under blue light for 2 weeks was similar to that under natural sunlight for 6 weeks. NAA treatment of the cutting surface significantly improved root growth under blue light as compared with non-NAA treatment. The effects of NAA treatment on growth under other light types were not significantly different. However, longer exposure to blue light resulted in leaf etiolation of older leaves. Our results indicate that use of blue LEDs to irradiate basil cuttings significantly reduced the time required for both root formation and the development of conventional cuttings compared to other light types.