Phenotypic Diversity and QTL Detection of Individual Sugars in RosBREED Apple Germplasm

Apple (Malus × domestica Borkh.), a member of the Rosaceae family, is the fourth most important global fruit crop based on the annual production. Washington State accounts for approximately 60% of total U.S. dessert apple production. There is an increasing demand for new apple cultivars in the world, but apple breeding is very time-consuming, and can take almost 20 years from the initial cross to cultivar commercialization. DNA marker-assisted methods are improving the efficiency of apple breeding by enabling more informed parent combinations for the initial cross and selecting desired genotypes at the early seedling stage. Improvement of fruit quality is the principal goal of the apple breeding program in Washington State University and sweetness is one of the most important fruit traits in apples. Sensory sweetness is the human response to the complex of sucrose, fructose, glucose and sorbitol contained in the apple fruit. The relative contribution of individual sugars to sensory sweetness will determine which QTL to focus on and possible haplotypes for the development of usable markers.

In USDA-NIFA funded RosBREED project, almost 1,000 individuals from three different apple breeding teams (Cornell University, University of Minnesota and Washington State University) have been phenotyped using standardized protocol in both 2010 and 2011 and the same individuals have genotyped to generate a highly saturated SNP linkage map. Four individual sugars have been measured from the germplasm using gas chromatography-mass spectrometry (GC-MS). QTLs linked to sugars were detected on apple chromosomes1,2 and 16, and used for marker-assisted apple breeding.