Genetic Diversity and Classification of Malus Germplasm Using Simple Sequence Repeats (SSRs)

To assess genetic diversity and study genetic relatedness in a wide collection of Malus germplasm, microsatelites or simple sequence repeats (SSRs) were used to screen this collection.  A total of 114 accessions from the Malus core collection, maintained at the University of Illinois, were evaluated for several phenotypic traits and genotyped using apple SSR markers.  Data on several phenotypic traits were recorded, including fruit size, fruit weight, and fruit shape; moreover, data on several fruit quality characteristics were also determined, including sugar content (ºBrix), titratable acidity (TA), and firmness.  Each of the accessions was then genotyped using a single robust SSR marker from each of the 17 different linkage groups.  These SSR markers were selected on the basis of their high levels of polymorphisms, reproducibility, and their amplification across wide genetic Malus backgrounds.  Multiple alleles were amplified across all screened accessions, thus allowing for analysis of genetic relatedness in this material.  Phenotypic and genotypic data were used to characterize the genetic diversity in this material and to identify markers associated with some of the phenotypic traits analyzed.