Elucidation and characterization of QTLs for Russet formation on apple fruit in ‘Honeycrisp’-derived breeding germplasm

Russet formation in apples ( Malus domestica Borkh.) is a superficial skin disorder that detracts from fruit appearance and therefore is a breeding target in many apple scion breeding programs. Previous studies have reported quantitative trait loci (QTLs) for russet formation, but these results have been limited to a narrow genetic background, which reduces breeding utility. In this study, 14 breeding parents were represented in 13-full sib families, nine of which were ‘Honeycrisp’-derived while the other four were derived from ‘Minneiska’, an offspring of ‘Honeycrisp.’ Two previously reported QTLs, on linkage group (LG) 2 and LG6, were confirmed and characterized for the first time in ‘Honeycrisp’-derived germplasm. Five other putative QTLs were also detected. The QTLs characterized in this study could be targeted for DNA test development to be used in marker-assisted selection. Non-additive interactions were observed at and between the LG2 and LG6 QTLs. Future work should include validation of QTL and haplotype effects in other germplasm, development of trait-predictive DNA tests for use in apple breeding programs, and exploration of genome-wide prediction models for russet formation.