Phenotypic Diversity of Individual Sugars, Soluble Solids Content, and Acidity in Rosbreed Apple Germplasm

Marker-assisted breeding has been applied in traditional apple breeding programs to increase breeding efficiency and reduce costs of time, land, and labor by testing important parental genotypes to determine the best genetic combinations, discarding seedlings with undesirable traits, and verifying pedigree. In order to more efficiently and accurately identify molecular markers of interest, an extensive germplasm set representing the breeding program is essential.  As part of the RosBREED project enabling marker-assisted breeding in Rosaceae, an apple reference germplasm set (crop reference germplasm and breeding pedigree germplasm sets) of 747 individuals was established based on the pedigree and allele representation of important parental cultivars, selections and seedlings at the apple breeding programs at Cornell University, University of Minnesota, and Washington State University. Sweetness is one of the important quality traits in apples, and sensory sweetness is a complex human sensation affecting by sweetness, acidity, and aroma. Phenotypic data of sensory sweetness, soluble solids content (SSC), and titratable acidity (TA) were collected using a standardized phenotyping protocol at all three sites at harvest, and after 10 weeks  and 20 weeks of cold storage plus 1 week shelf life in 2010, 2011, and 2012. In addition, flesh concentrations of individual sugars (fructose, glucose, sucrose, and sorbitol) and malic acid from 735 and 625 individuals at harvest in 2010 and 2012, respectively, were also estimated using GC-MS. The ranges and means of these traits vary among three locations to account for each unique germplasm set and different growing environments. For example, concentrations of individual sugars are relatively higher in Washington State than the other two sites at harvest in 2011. The phenotypic data for SSC and TA in RosBREED apple crop reference set are available for the public in the Breeder Toolbox at the Genome Database for Rosaceae (GDR) (www.rosaceae.org).