Citation: Halmagyi, A.; Coste, A.; Deliu, C.; B ˘ acil˘ a, I. High Frequency Direct Organogenesis in Five Romanian Tomato (Lycopersicon esculentum Mill.) Cultivars. Horticulturae 2023, 9, 411. https://doi.org/10.3390/ horticulturae9030411 Academic Editors: Orsolya Borsai, Clapa Doina, Mirela Irina Cordea, Monica Harta, Songling Bai and Zhihui Cheng Received: 10 February 2023 Revised: 20 March 2023 Accepted: 20 March 2023 Published: 22 March 2023 Copyright: © 2023 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/). horticulturae Article High Frequency Direct Organogenesis in Five Romanian Tomato (Lycopersicon esculentum Mill.) Cultivars Adela Halmagyi, Ana Coste * , Constantin Deliu and Ioan Băcilă NIRDBS, Institute of Biological Research Cluj-Napoca, 48 Republicii Street, 400015 Cluj-Napoca, Romania * Correspondence: ana.coste@icbcluj.ro Abstract: Tomato (Lycopersicon esculentum Mill.) as the most economically important vegetable crop worldwide has been investigated intensively for the development of new and improved varieties. Most of these technologies require efficient protocols for in vitro regeneration and propagation of plant material. In the present study, an efficient and reproducible in vitro regeneration system for five Romanian tomato genotypes (cvs. ‘Capriciu’, ‘Darsirius’, ‘Kristin’, ‘Pontica’ and ‘Siriana’) has been established. The tomato genotypes were selected based on their horticultural and economically valuable traits. To study the in vitro morphogenic response, various explants, such as cotyledons, cotyledonary nodes, hypocotyls, leaf explants, internodes, stem nodes and apical buds have been selected. The highest efficiency in terms of direct shoot organogenesis was obtained in cv. ‘Capriciu’ (98% for apical buds and 94% for stem nodes) on culture media with zeatin and indole-3-butyric acid. One advantage of this regeneration procedure is beside its feasibility in handling, the high percentage of regenerated shoots and their rooting. The present protocol contributes to the existing information regarding the response of tomato cultivars to in vitro culture conditions. Keywords: genotypes; plant growth regulators; regeneration 1. Introduction Plant tissue cultures are used for various purposes among them clonal multiplication, conservation, international germplasm exchange or to create improved commercial cul- tivars [1]. Tissue culture technology is an important requisite in breeding programs for development and selection of new cultivars with improved horticultural traits. In recent decades, genetically uniform varieties have replaced cultivars and landraces in traditional agro-ecosystems well adapted to local conditions, therefore it is important to preserve these cultivars which may be further used for selection of quality features [2]. Tomato (Lycopersicon esculentum Mill.), an important horticultural crop cultivated all over the world is known as a major source of essential nutrients [3]. It is one of the most extensively studied species not only for their importance as crop species but also as model system for molecular, physiological [4], genetic integrity [5,6], Raman spectroscopy [7], cryopreservation [6], ultrastructural studies [8], genetic transformation [9], and genome editing [10]. In the last decade the interest in tomato research has significantly increased especially due to its anti-cancer and anti-oxidative properties [11]. It is known that the improvement of various traits by conventional breeding requires long-lasting activity, while in vitro techniques can be a potential solution to assist breeding by manipulating desired traits. In vitro tomato cultures have been successfully used in some biotechnological appli- cations [12–14], for breeding purposes by somatic embryos [15] and to obtain virus-free high-value commercial cultivars [16]. In vitro regeneration of tomato shoots was induced by direct and indirect organogenesis [17–19] or through somatic embryogenesis [20]. There are many factors that affect the in vitro regeneration capacity of tomato plants, of which the most important are: the genotype, explant type, culture media composition, concentration Horticulturae 2023, 9, 411. https://doi.org/10.3390/horticulturae9030411 https://www.mdpi.com/journal/horticulturae