Identification of weeping crabapple cultivars by microsatellite DNA markers and morphological traits

Ornamental crabapples are small landscape trees with charming flowers, colourful fruits and many growth forms. The first weeping crabapple cultivars, Malus prunifolia 'Pendula' and 'Pendula Nova', were described in Sweden around 150 years ago. Our study was aimed at identification and characterization of weeping crabapple clones by microsatellite markers and morphological traits. We analysed 13 Swedish and Finnish trees and 8 reference accessions including M. prunifolia 'Pendula' and three international cultivars belonging to its progeny. The 21 trees represented 13 distinct genotypes. Five local trees were identified as the historical 'Pendula', assumed to be extinct from the nursery trade. On the basis of morphological traits and historical records, two old Swedish trees were concluded to represent 'Pendula Nova'. The authenticity of the trees could not be confirmed by DNA markers because no known plant of the old cultivar was found in botanical collections. The Finnish clone 'Hyvingiensis' proved unique among the crabapple accessions studied. 'Hyvingiensis' was probably raised from seed at the Finnish State Railways Nurseries about 110 years ago. Several mislabellings were revealed among both the local and the reference samples. A novel identification key was created to aid discrimination between the clones by their morphological traits. A combination of DNA fingerprints, comparison of morphological traits and tracing information in relevant archives and old garden literature proved useful for solving the origin and identity of weeping crabapples. The results contribute to conservation of garden plants and stabilization of horticultural nomenclature.