ORIGINAL ARTICLE Genetic Resources (2022), 3 (6), 22–37 DOI: 10.46265/genresj.HJIF8839 https://www.genresj.org ISSN: 2708-3764 Morphological characterization of 23 Malus domestica Borkh cultivars from central Spain Alberto Arnal * , a, b , Almudena L´ azaro a and Javier Tard´ıo a a Departamento de Investigaci´ on Agroalimentaria. IMIDRA. Autov´ıa A2, km 38.2, Aptdo. 127, 28800, Alcal´ a de Henares, Madrid, Spain b Departamento de Biotecnolog´ıa-Biolog´ıa Vegetal. E.T.S.I.A.A.B, Universidad Polit´ecnica de Madrid, Madrid, Spain Abstract: The purpose of this work was to morphologically characterize an apple tree collection composed of 67 individuals from 41 accessions belonging to 23 old Spanish apple cultivars (Malus domestica Borkh) alongside 9 reference cultivars. The studied germplasm was collected previously in rural areas of central Spain (Sierra Norte de Madrid and Tagus river basin) and it was analyzed through 67 descriptors mainly from IBPGR and UPOV. We found a very high morphological diversity in the studied old apple cultivars, as 48% of the descriptors (most of them devoted to fruit traits) were significantly different between types of cultivars. In addition, the sample cultivars resulted clearly distinct from reference cultivars in multivariate analysis. In general, no particular structure was found in old cultivars, but a strong differentiation of ‘Agridulce’ and ‘Hojancas’ is reported due to their bigger fruits. Our results support the molecular analysis and call for further analysis of the local apple germplasm and long-term conservation actions. Keywords: Apple genetic resources, old apple cultivars, phenotype, multivariate analysis Citation: Arnal, A., L´ azaro, A., Tard´ıo, J. (2022). Morphological characterization of 23 Malus domestica Borkh cultivars from central Spain. Genetic Resources 3 (6), 22–37. doi: 10.46265/genresj.HJIF8839. © Copyright 2022 the Authors. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Introduction The apple tree (Malus domestica Borkh.) is the most important temperate fruit tree crop, with more than 126 million tonnes harvested worldwide in 2020 (FAO, 2022). Such production is in line with the Second Report on the State of the World’s Plant Genetic Resources for Food and Agriculture (FAO, 2010), which reported Malus L. genetic resources to be among the largest ex situ collections. Morphological characterization of Malus has been essential for an adequate description of germplasm collections, for breeding programmes (Boˇzovi´c et al, 2015) and taxonomic studies (H¨ ofer et al, 2014; Wagner et al, 2014). Currently, although the information provided by genetic markers (such as microsatellites) is preferred against phenotyping due to their stability and economy (Reddy et al, 2002; Ban et al, 2014), the study of agricultural germplasm by morphological traits is still * Corresponding author: Alberto Arnal (alberto.arnal@madrid.org) relevant and useful in diversity analysis (Boˇzovi´c et al, 2015; Kir´ aly et al, 2015; Kumar et al, 2018). As a result, apple morphological descriptions were conducted in Bosnia and Herzegovina (Gaˇsi et al, 2011), Canada (Watts et al, 2021), Hungary (Kir´ aly et al, 2015), India (Dolker et al, 2021), Iran (Farrokhi et al, 2013), Italy (Martinelli et al, 2008), the Kashmir Valley (Dar et al, 2015), Macedonia (Kiprijanovski et al, 2020), Montenegro (Boˇzovi´c et al, 2015), Serbia (Mratini´c et al, 2012) and Turkey (Karatas, 2022), reporting high morphological diversity. The most common morphological descriptors used in those works belong to international guidelines such as IBPGR (1982) and UPOV (2005) and they focus on fruit characteristics because sensorial characteristics and consumer demand focus on fruits (Pereira-Lorenzo et al, 2018). In Spain, several studies also reported great phe- notypic apple diversity (Royo and Itoiz, 2004; Ramos- Cabrer et al, 2007; Santesteban et al, 2009; P´erez- Romero et al, 2015), but they did not include old cul- tivars from some central regions. This lack of informa- Received: 20.12.2021 Accepted: 24.05.2022 Published online: 31.08.2022