Candidate genes and QTLs for sugar and organic acid content in peach [Prunus persica (L.) Batsch]

The identification of genes involved in variation of peach fruit quality would assist breeders in creating new cultivars with improved fruit quality. Major genes and quantitative trait loci (QTLs) for physical and chemical components of fruit quality have already been detected, based on the peach [Prunus persica (L.) Batsch] cv. Ferjalou Jalousia(R) (low-acid peach) x cv. Fantasia (normally-acid nectarine) F, intraspecific cross. Our aim was to associate these QTLs to structural genes using a candidate gene/QTL approach. Eighteen cDNAs encoding key proteins in soluble sugar and organic acid metabolic pathways as well as in cell expansion were isolated from peach fruit. A single-strand conformation polymorphism strategy based on specific cDNA-based primers was used to map the corresponding genes. Since no polymorphism could be detected in the Ferjalou Jalousia(R) x Fantasia population, gene mapping was performed on the almond [Prunus amygdalus (P dulcis)] cv. Texas x peach cv. Earlygold F-2 interspecific cross from which a saturated map was available. Twelve candidate genes were assigned to four linkage groups of the peach genome. In a second step, the previous QTL detection was enhanced by integrating anchor loci between the Ferjalou Jalousia(R) x Fantasia and Texas x Earlygold maps and data from a third year of trait assessment on the Ferjalou Jalousia(R) x Fantasia population. Comparative mapping allowed us to detect a candidate gene/QTL co-location. It involved a cDNA encoding a vacuolar H+-pyrophosphatase (PRUpe;Vp2) that energises solute accumulation, and QTLs for sucrose and soluble solid content. This preliminary result may be the first step in the future development of marker-assisted selection for peach fruit sucrose and soluble solid content.