Sustainability 2022, 14, 9272. https://doi.org/10.3390/su14159272 www.mdpi.com/journal/sustainability Article Primary Growth Effect of Salix viminalis L. CV. Inger and Tordis in Controlled Conditions by Exploring Optimum Cutting Lengths and Rhizogenesis Treatments Sorin Daniel Vâtcă 1 , Ștefania Gâdea 1,† , Roxana Vidican 2 , Mignon Șandor 3, * ,† , Vlad Stoian 2 , Anamaria Vâtcă 4 , Adrian Horvath 5 and Valentina Ancuța Stoian 1, * ,† 1 Department of Plant Physiology, Faculty of Agriculture, University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, Calea Mănăştur 3-5, 400372 Cluj-Napoca, Romania; sorin.vatca@usamvcluj.ro (S.D.V.); stefania.gadea@usamvcluj.ro (Ș.G.) 2 Department of Microbiology, Faculty of Agriculture, University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, Calea Mănăştur 3-5, 400372 Cluj-Napoca, Romania; roxana.vidican@usamvcluj.ro (R.V.); vlad.stoian@usamvcluj.ro (V.S.) 3 Department of Ecology, Faculty of Agriculture, University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, Calea Mănăştur 3-5, 400372 Cluj-Napoca, Romania 4 Department of Management and Economics, Faculty of Animal Science and Biotechnologies, University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, Calea Mănăştur 3-5, 400372 Cluj-Napoca, Romania; anamaria.vatca@usamvcluj.ro 5 Department of Environmental Engineering, Faculty of Agriculture, University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, Calea Mănăştur 3-5, 400372 Cluj-Napoca, Romania; adrian.horvath@rebina.ro * Correspondence: sandor.mignon@usamvcluj.ro (M.Ș.); valentina.stoian@usamvcluj.ro (V.A.S.) † These authors contributed equally to this work. Abstract: The major disadvantage of setting up a willow coppice is the low survival rate, which reduces economic efficiency and crop sustainability. The aim of this research was to test, under controlled conditions, the impact of water, gibberellic acid A3 (0.05%), and humic acid (0.2%) on the growth and development of two willow clones. Under humic acid treatment, 20 cm cuttings of the Tordis clone developed up to 15 roots, and 25 cm cuttings developed more than 23. In comparison, water stimulated more than 15 roots for both 20 and 25 cm cuttings. Gibberellins acted as an inhib- itor, especially on the roots, and the cuttings dried out from the top to the middle, with weak devel- opment of shoots and callus formation. For both clones, the highest number of active buds was observed on 20 and 25 cm cuttings grown in water, with more than four for Inger and more than seven for Tordis. Root development of the Inger clone had a maximum of eight for 25 cm cuttings grown in water; it was three times lower in the same variant of Tordis and two times lower for the Tordis clone with humic acid treatment. In general, Inger cuttings of 15 and 25 cm highlighted a delayed root formation when humic acids and gibberellins were applied. In controlled condition experiments, the Tordis clone was more suitable owing to its higher development and increased growth stability. Keywords: callus formation; gibberellins; growth; humic acid; roots; shoots; willow 1. Introduction Given the current energy crisis worldwide, Romania is focusing on alternative en- ergy sources mainly for biomass production of bioethanol or pellets. In this context, wil- low (Salix viminalis spp.) is intensively targeted because of its low cost and high yield; it is easily converted into alternative energy to reduce the use of conventional sources such as fossil fuel, coal, or crude oil. Therefore, this species represents a valuable green and Citation: Vâtcă, S.D.; Gâdea, Ș.; Vidican, R.; Șandor, M.; Stoian, V.; Vâtcă, A.; Horvath, A.; Stoian, V.A. Primary Growth Effect of Salix vimi- nalis L. CV. Inger and Tordis in Con- trolled Conditions by Exploring Op- timum Cutting Lengths and Rhizogenesis Treatments. Sustainability 2022, 14, 9272. https://doi.org/10.3390/su14159272 Academic Editors: Ali Mohammadi and Georgios Koubouris Received: 30 May 2022 Accepted: 26 July 2022 Published: 28 July 2022 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional claims in published maps and institu- tional affiliations. Copyright: © 2022 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con- ditions of the Creative Commons At- tribution (CC BY) license (https://cre- ativecommons.org/licenses/by/4.0/).