Abstract
Apple (Malus × domestica Borkh.) is the most widely grown permanent fruit crop of temperate climates. Although commercial apple growing is based on a small number of globally spread cultivars, its diversity is much larger and there are estimates about the existence of more than 10,000 documented varieties. The varietal diversity can be described and determined based on phenotypic characters of the external and internal traits of fruit, which, however, can be modulated by environmental factors. Consequently, molecular methods have become an important alternative means for the characterisation of apple cultivar diversity. In order to use multilocus microsatellite data for determination of unidentified or misidentified apple varieties, a database with molecular genetic fingerprints of well-determined reference cultivars needs to be available. The objective of the present work was to establish such a database that could be applied for the molecular genetic determination of a large number of historic and modern, diploid and triploid apple cultivars. Based on the analysis of more than 1600 accessions of apple trees sampled in 37 public and private cultivar collections in different European countries at 14 variable microsatellite loci, a database with 600 molecular genetic profiles was finally obtained. The key criterion for considering a molecular genetic profile as confirmed and for including it into the reference database was that at least two accessions of the same cultivar of different provenances generated an identical result, which was achieved for 98% of the apple cultivars present in the database. For the remaining genotypes, the cultivar assignment was supported by a parentage analysis or by comparison to molecular genetic profiles available in published works. The database is composed of 574 scion cultivars, 24 rootstock genotypes and two species of crab apples. Of the 574 scion cultivars, 61% were derived from historic or old cultivars, many of which were grown in Central Europe in the past. The remaining scion cultivars are currently grown or available in testing programmes and may gain importance in the future. In order to validate the genotyping data, parentage analysis was performed involving cultivars and rootstocks that arose after 1900, for which information about at least one parent cultivar was available from pomological and scientific literature and the molecular genetic profiles of the assumed parent(s) were also present in our database. This analysis revealed the presence of null alleles at locus COL, however, when excluding this locus, a mean genotyping error rate of only 0.28% per locus was revealed, which points to a high reliability of the dataset. The datasets with 14 and 13 loci (excluding locus COL) showed a high degree of discrimination power, with a combined non-exclusion probability of identity of 2.6 × 10−20 and 3.4 × 10−19. Five of the microsatellite loci analysed in the present study overlapped with another published dataset and after the application of conversion values, it was possible to align the allele lengths and compare the molecular genetic profiles of 20 randomly derived cultivars, which were analysed in both studies. This comparison evidenced an exact correspondence of the microsatellite profiles contained in the two datasets, further pointing to the accuracy of our database. Apart from its application to characterise genetic resources or to manage germplasm collections, the here presented database could serve as an important tool for quality control or as a useful instrument in breeding programmes.
Highlights
Apple (Malus × domestica Borkh.) is the most widely grown permanent fruit crop of temperate climates
Of the 600 genotypes included in the database, two belonged to the crab apples Malus baccata and M. floribunda, while the remaining were 24 rootstocks and 574 scion cultivars of M. domestica
Multilocus microsatellite analysis has become a standard tool for the assessment of genetic variability and the identification of duplicate accessions in order to contribute to a more efficient management of germplasm collections (e.g. Guarino et al 2006; Pereira-Lorenzo et al 2007; Routson et al 2009; van Treuren et al 2010; Garkava-Gustavsson et al 2013; Ferreira et al 2016; Gasi et al 2016; Urrestarazu et al 2016; Larsen et al 2017; Testolin et al 2019)
Summary
Apple (Malus × domestica Borkh.) is the most widely grown permanent fruit crop of temperate climates. In Europe, apple was cultivated on an area of 473,500 ha in 2017 and it represented the most common fruit tree species (Eurostat 2019). The domestic apple is an interspecific hybrid originating from Central Asia that had been cultivated since antiquity (Janick 2005; Cornille et al 2014). Some of the cultivars were grown locally, while others were distributed over larger geographic areas in Europe (Hartmann 2015). Trees, scionwood or apple seeds from European countries were disseminated to other continents during the colonisation of the New World, where the selection of new cultivars had been continued (Janick 2005; Volk and Henk 2016)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
