**1. Introduction**

Sweet potato (*Ipomoea batatas* (L.) Lam), a member of the bindweed family (*Convolvulaceae* Juss.), is well known for its food, medicinal, and industrial value [1–3]. More than 5000 years ago, this species was first domesticated in the Americas. It is estimated that more than 7000 sweet potato cultivars have been bred to date. Sweet potatoes are considered one

**Citation:** Kirakosyan, R.N.; Kalashnikova, E.A.; Abubakarov, H.G.; Sleptsov, N.N.; Dudina, Y.A.; Temirbekova, S.K.; Khuat, Q.V.; Trukhachev, V.I.; Sumin, A.V. Influence of Mineral Treatment, Plant Growth Regulators and Artificial Light on the Growth of Jewel Sweet Potato (*Ipomoea batatas* Lam. cv. Jewel) In Vitro. *Life* **2023**, *13*, 52. https://doi.org/10.3390/ life13010052

Academic Editors: Hakim Manghwar and Wajid Zaman

Received: 10 November 2022 Revised: 6 December 2022 Accepted: 21 December 2022 Published: 24 December 2022

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

of the most important root crops after potatoes and cassava [4], especially in developing countries in Latin America, Southeast Asia, and Africa [5]. In these countries, sweet potato is a main food crop for the people because of its richness with healthy proteins, vitamins, antioxidants, and minerals [6,7]. Studies have shown that this species possesses a number of pharmaceutical properties, such as antibacterial, antioxidant, anticancer, anti-inflammatory, and antiulcer activities [8–10]. In traditional medicine in many countries, sweet potato is used to treat diabetes, anemia, hypertension, stomach cancer, cardiovascular disease, allergies, constipation, eye disease, arthritis, dengue fever, and nausea [6,10–15]. On the other hand, sweet potato can be used in cooking, as well as in different industrial foods production [16–18].

Traditionally, sweet potato cultivars have been propagated by vegetative propagation using stem cuttings or tubers [7,19]. However, this method has certain limitations, such as slow propagation speed, being time-consuming, and being season-dependent. On the other hand, stem cuttings or tubers used for this method often accumulate pathogens (such as nematodes, insect pests, and pathogens that cause black rot, scurf, and stem rot) and can be spread from one generation to the next, causing great losses in yield and the production of poor-quality tubers [3,7,19]. Therefore, if large-scale, uniform, and disease-free plant material is required for production, this method is not always suitable [3,7]. On the other hand, the seeds of sweet potato are only used to breed and develop new cultivars of sweet potatoes because of their highly heterozygous nature [20]. In order to overcome the limitations, biotechnological methods using plant tissue culture techniques have been used for the commercial scale-up of many cultivars of sweet potato. In previous reports, several types of explants, e.g., nodal segment, axillary shoot, and shoot tip from mature or in vitro plants, have been used as explants for in vitro shoot proliferation of sweet potato cultivars [21–39]. In there, nodal segments have been recognized as the best or most commonly used explants for the micropropagation of various sweet potato cultivars, e.g., 'Carmen Rubin' and 'White Triumph' [32], 'Gaozi No.1' [27], 'Naruto Kintoki' [40], 'KSP 36' and 'KEMB 36' [41], and 'Abees' [4]. However, little is known about the micropropagation of jewel sweet potato, which is dubbed the 'sweet potato queen' due to its high nutritional value and delicious taste with all processing methods. This sweet potato cultivar was bred in 1970 at North Carolina State University. To date, jewel has become one of the most commonly grown sweet potato cultivars, its tubers are characterized by tan skin and orange flesh and that is considered a rich source of provitamin A carotenoid [42,43].

In fact, the efficacy of micropropagation techniques depends on a variety of factors, of which three important factors are culture medium, plant growth regulators (PGRs), and artificial light sources (type and intensity). In most reports, Murashige and Skoog (MS) [44] base medium was reported to be the most suitable medium for shoot initiation, shoot proliferation, and rooting in sweet potato cultivars [21–39]. However, in some sweet potato cultivars, 1/2MS medium has been found to be more suitable for shoot proliferation and rooting, e.g., 'purple flesh sweet potato' [37] and 'red-peeled sweet potato' [4]. Most of the authors have shown that the medium without any PGRs is not suitable for in vitro shoot regeneration. In sweet potato, nutrient media supplemented with cytokinins in combination with auxins were reported to be the best for in vitro shoot proliferation [21–23,26,37]. Besides the above two factors, the type and intensity of artificial light also affect the micropropagation of sweet potatoes. Yang et al. [45] found that the different ratios of photosynthetic photon flux (PPF) of red LED (R) and PPF of blue LED (B) had different effects on the growth of sweet potato plantlets in vitro.

The aim of the present study was to determine the effects of different PGRs, different MS salt concentrations, and different artificial light conditions on the induction, proliferation, and growth of in vitro *Ipomoea batatas* 'Jewel' shoots obtained from the axillary bud and shoot tip explants.

#### **2. Materials and Methods**

#### *2.1. Plant Material Preparation*

The work was carried out at the Department of Biotechnology of the Russian State Agrarian University—Moscow Agricultural Academy named after K. A. Timiryazev (Moscow, Russia). All work on sterilization, introduction into culture in vitro, and further work on the study of callogenesis and morphogenesis were carried out in aseptic conditions of laminar hood flow (Biokom). The object of the study was explants of sweet potato (*Ipomoea batatas* Lam.), cultivar Jewel (USA), provided by the Federal Research Center for Potato named after A. G. Lorch.

Before being placed in vitro, the jewel sweet potato tubers were placed in water to activate the dormant meristem. On the 7th day, the shoots began to form, and on the 21st day, they reached 10–12 cm. 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 experiments. The explants' surface was sterilized with a 0.1% solution of mercuric chloride (HgCl2). They were soaked in the solution for 5 min and then rinsed with sterile distilled water [4].
