The 2012 ASHS Annual Conference

Apple (Malus × domestica Borkh.), a member of the Rosaceaefamily, is the fourth most important global fruit crop in the world based on 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-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 candidate genes for the development of usable markers. In USDA–NIFA funded RosBREED project, almost 1000 apple individuals from three different apple breeding teams (Cornell University, University of Minnesota, and Washington State University) have been phenotyped using standard protocol at harvest, 10-week and 20-week cold storage with 1-week shelf life in both 2010 and 2011 and used to generate a highly saturated SNP linkage map. Four individual sugars have been measured at each time from the germplasm set using gas chromatography. Principal component analysis (PCA) showed that fructose and sucrose have higher correlations with sensory sweetness in harvest samples from Washington State University, 0.51 and 0.50, respectively. QTLs linked to sweetness will be detected on apple chromosomes 3, 6, 8, 9, and 14, and used for marker-assisted apple breeding.