Phenotypic evaluation and characterization of a collection of Malus species

A collection of 337 Malus accessions representing 46 species of the Fruit Genebank in Dresden-Pillnitz, Germany, were evaluated for 64 morphological and phenological traits to proof the classification of the accession and to analyze genetic relationships. Morphological characteristics were determined for the whole tree, shoots, leaves, flowers and fruits. Data were subjected to principal component analysis (PCA), and a dendrogram was constructed to demonstrate morphological relationship. According to PCA the most important variables integrated in the first principal component were mainly fruit descriptors and three traits characterizing pubescence (1 year old shoot, leaf blade, and pedicel). Cluster analysis clearly separated the accessions in Malus series. The results showed the polyphyletic origin of the section Sorbomalus. The North American apple species, M. fusca, was closely related to the species contributing to the East Asian center of the genus origin. The relict species of the European continent (M. trilobata) was grouped in near distance to the North American species belonging to section Chloromeles. The species of Sieversinae and Baccatae dominated in one main cluster indicating their close relatedness. Most of M. 9domestica accessions were grouped with M. sieversii and M. orientalis; this supports the Sievers apple as an ancestor of domesticated apple. The morphological evaluations in this study indicated a high level of phenotypic diversity in the genebank collection. These phenotypical data will increase the feasibility of prioritizing accessions based on the uniqueness of desirable morphological traits.