Detection of QTL for apple fruit acidity and sweetness using sensorial evaluation in multiple pedigreed full-sib families

Acidity and sweetness are important qualities for apple breeders and understanding their genetic regulation can improve the breeding process. In previous QTL studies, fruit quality assessments were performed using instrumental measurements, leading to the identification of two major QTL Ma and Ma3. Here, we use sensorial data to investigate the role of known and unknown genetic factors in the perception of acidity and sweetness in three pedigreed full-sib families. For 2 years, these families were phenotyped by a trained panel, at harvest and after 2 months of cold storage, and genotyped with a new 50 K SNP array. FlexQTL^TM analyses using both an additive and an additive + dominance model resulted in the identification of Ma and Ma3 for acidity as well as sweetness, whereas the use of the additive model yielded decisive evidence for the discovery of two additional QTL on LG1 and LG6 for acidity. QTL genotypes were qualified as the inverse of each other, which indicates that individuals with the less-acidity alleles of Ma and Ma3 are perceived sweeter. Due to the genetic configuration in the families studied, resulting from a link with the Pale Green Disorder locus, no incomplete dominance effect could be detected for the Ma locus, although previously reported in the literature. For the Ma3 locus, however, an incomplete dominance effect (58%) is reported here for the first time. The Ma3 locus was also further confined to a 2–4-cM region and a predictive marker for this locus was identified.