Effect of LED light quality on in vitro shoot proliferation and growth of vanilla (Vanilla planifolia Andrews)

As an alternative to conventional lighting systems, light emitting diode (LED) has been demonstrated to be an artificial flexible lighting source for commercial micropropagation. The objective of this study was to determine the effects of different LED light quality on in vitro shoot proliferation and growth of Vanilla planifolia. To evaluate shoot proliferation, axillary bud cuttings (3 to 5 mm in diameter) of V. planifolia were used as explants and cultivated on Murashige and Skoog basal medium supplemented with 9.55 µM of 6-benzylaminopurine. To evaluate in vitro growth, unrooted shoots (2 cm in length) were used as explants cultivated on Murashige and Skoog basal medium without plant growth regulators. All explants were exposed to a 16 h photoperiod for 60 days under five different lights: fluorescent lamp, white LED, blue LED, red LED and blue plus red LED mixtures (Blue + Red = 1:1). The results indicated a clear increase in the number of shoots per explant under Fluorescent Lamp, White LED and Blue+Red LED light; these treatments produced more than 10 shoots. Shoot length was more than 3 cm in cultures under Blue, Red and Blue+Red (1:1) LEDs, and less than 3 cm in Fluorescent Lamp and White LEDs. Our results also showed that fresh weight, dry weight and dry matter were greatest in shoots under Blue+Red LED light. For shoot growth, plant height, number of leaves, number and length of roots, fresh weight, dry weight, dry matter and chlorophyll content were greater under Fluorescent Lamp and White LED. In conclusion, White or Blue+Red LED light may be used as an alternative light source for shoot proliferation, while White LED may be used for growth in vitro. These results demonstrate the effectiveness of light qualities using LEDs for micropropagation of V. planifolia. Key words: Light quality, micropropagation, orchid, chlorophyll.