Comparing Apples to Apples: A Genome-Wide Association Study of Sensory and Physical Attributes in Apple

Seventy diverse varieties of apple (Malus x. domestica) were analyzed for fruit quality traits and genotyped using genotyping-by-sequencing (GBS). In order to understand the differences in human perception of fruit quality between apple varieties, a trained sensory panel at the Vineland Research and Innovation Centre evaluated twenty commercial apple varieties grown in Canada and the United States and fifty heritage apple varieties grown in Vineland, Ontario. The apples were profiled in duplicate over two years and scored on 18 descriptors of taste, texture and flavour. As a means to calibrate the perceived fruit attributes against more commonly reported measures, the same varieties selected for sensory analysis were also evaluated for mechanical fruit firmness, flesh browning, ascorbic acid content, soluble solids content (°Brix) and titratable acidity. In the second year, the apple volatile compound profiles were determined using gas chromatography-mass spectrometry. For association mapping, GBS was conducted in duplicate on the seventy sample varieties, using the standard restriction enzyme ApeK1. Between 84 000 and 615 000 sequence tags per genotype were mapped onto the apple reference genome at a single position, and 104 000 single nucleotide polymorphism markers were identified with 5 % missing data before imputation. This poster presents our ongoing effort to map genome-wide associations between each sensory and physical attribute of the heritage and commercial apples and their underlying sequence variations. Relationships between the physical and perceived characters of apples in light of genomic selection for fruit quality are discussed.