| Summary: | We investigated the influence of different conditions (light composition and plant growth regulators (PGRs) in culture media) on the morphophysiological parameters of <i>Stevia rebaudiana</i> Bertoni in vitro and in vivo. Both PGRs and the light spectra applied were found to significantly affect plant morphogenesis. During the micropropagation stage of <i>S. rebaudiana</i>, optimal growth, with a multiplication coefficient of 15, was obtained in an MS culture medium containing 2,4-epibrassinolide (Epin) and indole-3-acetic acid (IAA) at concentrations of 0.1 and 0.5 mg L<sup>−1</sup>, respectively. During the rooting stage, we found that the addition of 0.5 mg L<sup>−1</sup> hydroxycinnamic acid (Zircon) to the MS medium led to an optimal root formation frequency of 85% and resulted in the formation of strong plants with well-developed leaf blades. Cultivation on media containing 0.1 mg L<sup>−1</sup> Epin and 0.5 mg L<sup>−1</sup> IAA and receiving coherent light irradiation on a weekly basis resulted in a 100% increase in the multiplication coefficient, better adventitious shoot growth, and a 33% increase in the number of leaves. <i>S. rebaudiana</i> microshoots, cultured on MS media containing 1.0 mg L<sup>−1</sup> 6-benzylaminopurine (BAP) and 0.5 mg L<sup>−1</sup> IAA with red monochrome light treatments, increased the multiplication coefficient by 30% compared with controls (white light, media without PGRs).
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