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The goal of the present study was to identify candidate genes (CGs) involved in fruit quality in peach that can be transferred to other Rosaceae species. Two cDNA libraries from fruit of the “Fantasia” peach cultivar, constructed at two stages of development, were used to generate a set of expressed sequence tag sequences. A total of 1,730 peach unigenes were obtained after clustering. Sequences and corresponding annotations were stored in a relational database and are available through a web interface. Fifty-nine CGs involved in fruit growth and development or fruit quality at maturity, focusing on sweetness, acidity, and phenolic compound content, were selected according to their annotation. Fifty-five primer pairs, designed from peach CG sequences and giving PCR products in peach, were tested in strawberry and 36 gave amplified products. Eight CGs were mapped in peach, 14 in strawberry, four in both species and confirmed the pattern of synteny already proposed using comparative mapping. In peach, the CGs are located in three linkage groups (3, 5, 7), and in strawberry they are distributed in all seven Fragaria linkage groups. Colocalization between some of these CGs and quantitative trait loci for fruit quality traits were identified and are awaiting confirmation in further analyses., This research was partially funded by the European ISAFRUIT Integrated Project. The ISAFRUIT project is funded by the European Commission under the Thematic Priority 5—Food Quality and Safety of the 6th Framework Programme of RTD (contract number FP6-FOOD-CT-2006-016279). We thank Dr. Christophe Rothan for his involvement in the construction of the cDNA libraries and Christel Renaud for her participation in the preparation of EST clones for sequencing. The strawberry research was supported in part with funds from the Spanish Ministry of Science and Innovation project INIA (RTA2007-00063-00-00) and Euroberry COST Action 863. JB was supported by a fellowship from AGAUR.

BackgroundAcidity is an essential component of the organoleptic quality of fleshy fruits. However, in these fruits, the physiological and molecular mechanisms that control fruit acidity remain unclear. In peach theDlocus controls fruit acidity; low-acidity is determined by the dominant allele. Using a peach progeny of 208 F2trees, theDlocus was mapped to the proximal end of linkage group 5 and co-localized with major QTLs involved in the control of fruit pH, titratable acidity and organic acid concentration and small QTLs for sugar concentration. To investigate the molecular basis of fruit acidity in peach we initiated the map-based cloning of theDlocus.ResultsIn order to generate a high-resolution linkage map in the vicinity of theDlocus, 1,024 AFLP primer combinations were screened using DNA of bulked acid and low-acid segregants. We also screened a segregating population of 1,718 individuals for chromosomal recombination events linked to theDlocus and identified 308 individuals with recombination events close toD. Using these recombinant individuals we delimited theDlocus to a genetic interval of 0.4 cM. We also constructed a peach BAC library of 52,000 clones with a mean insert size of 90 kb. The screening of the BAC library with markers tightly linked toDlocus indicated that 1 cM corresponds to 250 kb at the vicinity of theDlocus.ConclusionIn the present work we presented the first high-resolution genetic map ofDlocus in peach. We also constructed a peach BAC library of approximately 15× genome equivalent. This fine genetic and physical characterization of theDlocus is the first step towards the isolation of the gene(s) underlying fruit acidity in peach.