Effects of Light Quality on Vegetative Cutting and In Vitro Propagation of Coleus (Plectranthus scutellarioides)

Abstract

Coleus (Plectranthus scutellarioides) is an attractive and popular ornamental plant with propagation mainly achieved through vegetative cuttings. For commercial purposes, it is of interest to enhance the speed of establishment while maintaining high quality. Light quality has been shown to influence adventitious root development, so these experiments examined the effect of narrow-bandwidth light treatments on root growth and overall plant quality for seven coleus cultivars with vegetative cuttings in potting soil and one cultivar with shoot tip in vitro cultures onto Murashige and Skoog (MS) agar medium. During the 28 days of the propagation period, the cuttings grown under narrowbandwidth red light (R; 663.4 nm at peak) more than doubled in the adventitious root number compared with those under blue light (B; 445.7 nm at peak) and green light (G; 530.0 nm at peak) in five cultivars. R light also increased fresh weight of the cuttings by 55.6% more than G light. In comparison, the cuttings grown under G light yielded significantly lower root and shoot dry mass than other light treatments. R light cuttings showed more dry mass content (9.63%) than those under white light (W; 437.4 nm and 559.5 nm at peak) and G light (7.85% and 5.86%, respectively). A positive correlation (R 2 = 0.598, P < 0.001) was found between the formation of adventitious roots and gained fresh weight of cuttings. R light made the reddish color of leaves significantly stronger in most cultivars, whereas the cuttings exposed to G light became less vivid compared with other light conditions. When the shoot tips were propagated in vitro onto MS medium, R light treatment initiated the root development more rapidly than other lights, with significantly greater rooting rate (20.0% and 63.6%, respectively) at day 5 and 10. The shoot tips under R light also formed significantly more roots (12.3 per cutting) than those grown under narrow-bandwidth B light (5.8 per cutting). The shoot tips showed browning at an early stage and newly emerged leaves grew very compactly under B light. The combination of red and green light (R+G) increased more than twice as much roots and dry mass compared with W light. In addition, the R+G light led to morphological changes, including larger leaves and longer petioles and internodes than those in other light treatments. The exposure to R+G+B and B light made the shoots very compact for the 28 days of in vitro culture period and significantly increased the chlorophyll contents resulting in dark green leaves.

Gene expression profiling reveals the effects of light on adventitious root formation in lotus seedlings (Nelumbo nucifera Gaertn.)

“…Chen et al (2019) reported that root generation and overall plant development can be dramatically promoted under available light intensity conditions in Haworthia [41]. At the same time, light quality is shown to influence ARs in Coleus [42]. We found that different light intensities have various roles in the formation of ARs in lotus.…”

Effects of LED photoperiods and light qualities on in vitro growth and chlorophyll fluorescence of Cunninghamia lanceolata

“…In the 'Favorita' potato (Solanum tuberosum L.) plantlets cultured in vitro, plant height was the greatest under monochromatic red light, whereas root length and fresh weight were the greatest under R/B (8/2), and chlorophyll content was the greatest under R/B (7/3) [11]. Cho et al [12] pointed out that the combination of red and green light (R/G, 80/20) increased more than twice as much roots and dry mass compared with W in Coleus (Plectranthus scutellarioides) in vitro culture, and the exposure to the combination of red, green and blue light (R/G/B, 40/20/40) significantly increased the chlorophyll content. LED can influence the physiological process of plantlets cultured in vitro through the optimal combination of different light qualities, so as to promote the growth and improve the quality of plantlets.…”

Gene expression profiling reveals light regulation on adventitious root formation in lotus (Nelumbo nucifera Gaertn.)

“…report that root generation and development can be dramatically promoted under available light intensity condition in Haworthia [42]. At the same time, light quality is shown to influence ARs in number [43]. We found that different light intensity showed various roles on ARs formation in lotus.…”