*2.2. Experiment 1: Evaluate the Influence of Different MS Salt Concentrations on Induction and Growth of In Vitro Jewel Sweet Potato Shoots*

The shoot tips of 1.0 cm in length and stem pieces bearing the axillary buds of 1.5 cm in length from plantlets sprouting from tubers were used as explants for this experiment. Nutrient media containing different MS salts (MS: DUCHEFA, Haarlem, The Netherlands) were created. The addition of 4.4 g/L MS was determined as 100%. The ratios of MS salts used in nutrient media: 33% (1.45 g/L-MS1), 50% (2.2 g/L-MS2), 100% (4.4 g/L-MS), 150% (6.6 g/L-MS3) [46]. Sucrose was present at a concentration of 2% and agar of 0.8% in all variants of nutrient media. PGRs were not added to the nutrient medium in all treatments. The pH of the nutrient medium in all treatments was 5.8. The plants were cultivated in a well-lit growth chamber at 21–23 ◦C under a 16 h photoperiod provided by 3–3.5 klx white fluorescent lamps (OSRAM AG, Munich, Germany).

In vitro shoot growth indices (including shoot length and root length) in the treatments were measured after one and four weeks of culture.

#### *2.3. Experiment 2: Evaluate the Influence of Different PGRs on Proliferation and Growth of In Vitro Jewel Sweet Potato Shoots*

Shoots 1.5–2.0 cm in length from the first experiment were used as explants for this experiment. The MS2 semisolid media supplemented with a combination of 0.5 mg/L indole-3-acetic acid (IAA) with various cytokinins, including 0.5–2.0 mg/L 6-benzylaminopurine (BAP) (Sigma, Schnelldorf, Germany), 0.5–2.0 mg/L kinetin (Kn) (Merck, Darmstadt, Germany), and 0.1–1.0 mg/L thidiazuron (TDZ) (Russia), were used to culture the in vitro shoots. There were 2% sucrose and 0.8% agar in all media. In vitro shoots were subcultured to a fresh medium every 6 weeks. Visual observations were made after 45 days. The following indicators were taken into account: explants' survival rate, number of adventitious shoots per explant, shoot length, number of leaves per shoot, number of roots, and root length. The in vitro shoots were cultivated in a well-lit growth chamber at 21–23 ◦C under a 16 h photoperiod provided by 3–3.5 klx white fluorescent lamps (OSRAM AG, Munich, Germany).

*2.4. Experiment 3: Evaluate the Influence of Different Artificial Light Conditions on Induction and Growth of In Vitro Jewel Sweet Potato Shoots*

The shoots 1.5–2.0 cm in length from the first experiment were cultivated on two different types of media:


The in vitro shoots were cultivated in a light room with different lighting conditions. Three lighting treatments (differences in the ratio between the red (R) and blue (B) spectra) were used:

Treatment 1 (control): illuminators based on white LEDs with a color temperature of 3500 K and 6000 K and a monochromatic red LED with a peak of 660 nm (OSRAM AG brand, made in Germany).

Treatment 2a: multichannel illuminator based on white LEDs with a color temperature of 3500 K and 6000 K and monochromatic red (R) and blue (B) LEDs with peaks of 660 nm and 460 nm, respectively. The channel power of monochromatic LEDs was set in the ratio R: 70%/B: 30%.

Treatment 3a: multichannel illuminator based on white LEDs with a color temperature of 3500 K and 6000 K and monochromatic red and blue LEDs with peaks of 660 nm and 460 nm, respectively. The power of monochromatic LED channels was set in the ratio R: 30%/B: 70% [47].

In vitro shoot growth indices (including shoot length, root number, and root length) in the treatments were measured after 45 days of culture.

#### *2.5. Statistical Analysis of Experimental Data*

The experiments were arranged completely randomly and repeated three times. Mean values of all data were calculated using Microsoft Excel 2013 (Microsoft Corporation, Redmond, WA, USA). Analysis of variance (ANOVA) was performed in AGROS software (version 2.11, Russia) and means were compared using Fisher's least significant difference (LSD) test at a significance level of *p* ≤ 0.05.
