Pedigree-Based QTL Mapping Identifies Major Loci Associated to Fruit Sugar and Organic Acid Content in Apple

Fruit taste in apple (Malus × domestica) is one of the most important quality attributes and it is primarily determined by the balance between soluble sugars (mainly glucose, fruc- tose, and sucrose) and organic acid. The combination of these metabolites influences the consumer preference by impacting sweetness and acidity, and therefore represent the cen- tral target of several apple breeding programs. To investigate the genetic control of taste- related traits, a pedigree-based QTL (Quantitative Trait Loci) analysis (PBA) across six full-sub apple families was performed to identify major QTL-associated traits in elite ac- cessions. Bayesian statistics and Markov Chain Monte Carlo (MCMC) methods revealed the presence of a common QTL for glucose and fructose on linkage group (LG) 16 as well as sugar-specific intervals mapped on LG1 for fructose and LG12 for glucose. Further- more, phenotypic sugars variation enabled also the identification of a QTL on LG4 for sucrose, while a QTL for malic acid content was detected on LG8. The LG16 was consistent between QTL-estimated genotypes, supporting its potential for marker-assisted selection. Our findings identified the genetic basis of apple taste traits, which can contribute to the development of improved apple cultivars with optimized sweetness and acidity balance and ultimately improved apple consumer appeal.