Preliminary QTLs Mapping For Sugars And Acids, And Impact Factors On Sugars And Acids In Peach (P. Persica (L.) Batsch) Fruit

The flavour quality of peach fruits is in a large part defined by their composition of soluble sugars and organic acids (sucrose, glucose, fructose, sorbitol, malic acid, citric acid, quinic acid and shikimic acid). A peach population derived from a clone of a wild peach (Prunus davidiand) by three generations of crosses with commercial nectarine varieties was analysed for agronomic and quality traits, and for molecular markers (RFLP, AFLP and SSR) in 2 locations over 2 successive years.Sugar and acid concentrations had considerable variations among genotypes. Location and year significantly influenced most sugar and acid concentrations, while through principal component analysis (PCA) the main correlations among them seemed not to be changed due to location or year. The first principal component was dominated by nearly all sugars and acids, and was a general flavour component; Glucose and fructose concentrations were closely correlated and had similar amount in most genotypes, while fructose concentration was lower than glucose concentration in about 20% of the genotypes; Malic and citric acid concentrations had positive correlations; Likewise, sucrose and sorbitol concentrations were positively associated. The number of QTLs for sugars and organic acids, and the additive effect and R" of each QTL were different with year, but some QTLs were detected in the two years. The QTLs for sucrose, glucose, fructose, sorbitol, citric acid and quinic acid were present on a linkage group 7; Except the positive QTLs for both glucose and fructose on the linkage group 7, a negative QTL with R~ 46.1% on linkage group 1 was detected for fructose; There were QTLs for both malic and citric acids on the linkage group 3 and 5.The relationships of sugars and organic acids with maturity date showed that glucose, fructose, sorbitol and shikimic acid concentrations had significantly positive correlations with maturity date, sucrose, malic acid and quinic acid concentrations had parabolic relationship with maturity date, and citric acid concentration had no obvious relationship with maturity date. Seasonal changes of glucose and fructose concentrations differed for the genotypes with early maturity date. For the genotypes with late maturity date, glucose concentration decreased and then tended to be constant, and fructose concentration decreased and then increased. Sorbitol concentration in the genotypes with late maturity date increased with fruit development, while it kept relatively stable in the genotypes with early maturity date. Malic acid concentration exhibited various patterns of seasonal changes with genotypes. Sucrose, citric, quinic and shikimic acid concentration varied as following: sucrose concentration increased with fruit development; citric acid concentration increased and then decreased; the levels of quinic and shikimic acids usually declined throughout fruit development. Generally, acid concentrations varied less strongly in the genotypes with late maturity date than with early maturity date. Principal Component Analysis (PCA) showed that in young immature fruits, glucose, quinic acid and shikimic acid concentrations were high, citric acid concentration increased to be highest in intermediate mature fruits, and mature fruits were characterized by increased sucrose, fructose and sorbitol concentrations.Mean sucrose, fructose, sorbitol, total sugar, soluble solids and quinic acid concentrations weresignificantly higher in nectarines than in peaches, while no significant difference was found in mean malic acid, citric acid and total acid concentrations between nectarines and peaches. Flesh colour did not influence sugars and acids significantly.Influence of the assimilate and water supply on seasonal variation of sugars and acids in peach (cv. Suncrest) was also studied. During the whole fruit development period, fruit with high assimilate supply had high sucrose and sorbitol concentrations, while assimilate supply had no significant influence on reduced sugar (glucose and fructose) concentration. At...