Genome-Wide Association Analyses Defined the Interplay between Two Major Loci Controlling the Fruit Texture Performance in a Norwegian Apple Collection (Malus × domestica Borkh.)

Abstract

Increasing consumption of apples (Malus domestica Borkh.) produced in Norway requires the availability of superior cultivars and extended marketability. Favorable texture and slow softening are important traits for consumer appreciation and postharvest performance. Apple texture has been well characterized using both sensory evaluation and instrumental assessments, and major quantitative trait loci (QTL) have been detected. With texture being targeted as an important trait and markers being publicly available, marker-assisted selection has already been implemented into several breeding programs. When focusing solely on a limited set of markers linked to well-investigated major QTLs, most minor-effect QTLs are normally excluded. To find novel potential SNP markers suitable to assist in selection processes, we selected a subset of accessions from a larger apple collection established in Norway based on the favorable alleles of two markers previously associated with texture, enabling the investigation of a minor part of the variance initially masked by the effect of major loci. The subset was employed to conduct a genome-wide association study aiming to search for associations with texture dynamics and retainability. QTL regions related to texture at harvest, postharvest, and for the storage index were identified on chromosomes 3, 12, and 16. Specifically, the SNPs located on chromosome 12 were shown to be potential novel markers for selection of crispness retention during storage, a valuable storability trait. These newly detected QTLs and underlying SNPs will represent a potential set of markers for the selection of the most favorable accessions characterized by superior fruit texture properties in ongoing breeding programs.