4. Discussion
Green light promoted stem elongation of potato plantlets in vitro(Table 2). Johkan et al. (2012) found that the elongation of shoots of Lactuca sativa was also the greatest under G. It has been reported that B inhibited the elongation of stems (Johkan et al., 2010). In this study, the addition of G to the combined spectrum of RB reduced the amount of B proportionally and likely alleviated the inhibition of stem elongation induced by B. Moreover, R630BG and FL caused the greatest increase in stem height, and it appeared that R630 and G had a synergistic effect on the elongation of stems. As previously reported, the combined spectrum of RB LEDs was found to be more conducive to stem diameter growth than FL (Duong et al., 2003;Nhut et al., 2003; Puspa et al., 2008). We observed similar results in our study; however, there was no significant difference in stemdia meters between the R630B and R660B treatments (Table 2), and tothe best of our knowledge there are no reports on the effects of R at different wavelengths on stem diameter. When G was added to the combined spectrum of RB, we found that R660BG had a greater effect