Genome-wide QTL Detection of Individual Sugars, Sensory Sweetness, and Soluble Solids Content in Apples

Apple (Malus × domestica Borkh.) is one of the most important fresh fruits in the world based on its annual production. Washington State is the leading apple producer in the United States, accounting for approximate 60% of the total production. The Washington State University apple breeding program was started in 1994 to develop new improved quality apple varieties focusing on fruit texture, flavor, and storability. The program uses DNA-based markers to assist in cross-planning and to improve the efficiency of selection, however, the number of available markers is still limited. Sweetness is an important but complex component of flavor, which has low heritability and is strongly influenced by environmental factors. As part of the RosBREED project, the phenotypic data of individual sugars (fructose, glucose, sucrose, and sorbitol), sensory sweetness, and soluble solids content (SSC) for 285 and 282 individuals were collected at harvest in 2011 and 2012, respectively. These individuals were genotyped with the RosBREED 8K apple SNP chip. FlexQTL^TM software was used to detect QTLs in Washington apple germplasm. Putative QTLs for fructose in Chromosome 1, 2, and 7, glucose in Chromosome 1, 6, 8, and 16, sucrose in chromosome 13, and sorbitol in chromosome 16 have been detected. These QTLs will be further studied for the development of functional markers to enable easy application in the Washington apple breeding program.