Simultaneous improvement of phytochemical content and eating quality in apples: estimates of genetic parameters

Modern apple cultivars tend to have significantly lower phenolic content than wild species and heritage cultivars. Although the phytochemical makeup of apple fruit affects important traits, such as nutrition, flavour, texture and disease resistance, phytochemical-based breeding strategies for apple improvement are lacking. We studied the relationships between fruit phenolic content and sensory traits in a seedling population derived from crosses between the domesticated and wild apple species. We also investigated the potential of genomic selection for breeding new high-health cultivars faster. Phenolic content, sensory traits, sugar levels, and a stable vitamin C glycoside (ascorbic acid 2-beta-glucoside [AA-2βG]) were assessed to estimate the genetic parameters of these traits. Phenolic compounds (chalcones, flavanols [FLAVA], cinnamic acids), triterpenoids (TRITP), carbohydrates (CARBO), AA-2βG, and sensory traits (astringency [ASTR], sourness [SOUR]) were found to be moderately heritable (h² = 0.35–0.50), while fructose–glucose ratio (FGRAT), fruit size (SIZE), and overall eating quality (EQUAL) were highly heritable (h² > 0.75). FGRAT was strongly correlated (> 0.70) with sweetness (SWEET) and EQUAL. Phenolics and AA-2βG were positively correlated, but both displayed moderate negative correlations with EQUAL. TRITP content displayed a moderate positive correlation with EQUAL and negative correlation with SOUR and ASTR. The accuracy of genomic prediction ranged from 0.50 (FLAVA) to 0.90 (SIZE) and was highly correlated with trait heritability. The knowledge derived from this study can assist in designing DNA-based fast-breeding strategies for simultaneous improvement of phytochemicals and sensory traits.