Identification of unknown apple (Malus × domestica) cultivars demonstrates the impact of local breeding program on cultivar diversity

Abstract

Apple (Malus × domestica Borkh.) trees, either abandoned or cared for, are common on the North American landscape. These trees can live for decades, and therefore represent a record of large- and small-scale agricultural practices through time. Here, we assessed the genetic diversity and identity of 330 unknown apple trees in northern Minnesota with 9 simple sequence repeat (SSR) markers. The unknown (not identified by cultivar name) trees were compared to > 1000 named cultivars in the U.S. Department of Agriculture Plant Genetic Resources Unit Malus collection and also to each other to identify repeated genotypes. Overall, the 330 unknown trees had high diversity (average He = 0.75), and consisted of 264 unique genotypes. A total of 76 of the unknown trees were matched to 20 different named cultivars, and these cultivars were mainly derived from either the local breeding program at the University of Minnesota, or were Russian cultivars imported for horticulture in the northern US. This study demonstrates the importance of local breeding programs, and also the challenges associated with identifying clones in a genetically diverse crop like apple.