Genetic and QTL analysis of sugars and acids content in sweet cherry (Prunus avium L.)

Abstract Sweet cherry is very appreciated by consumers because of its attractive appearance and taste, which is determined by the balanced sweet–sour flavor. In this work, the genetics of soluble solid content (SSC), titratable acidity (TA), sugars, and organic acids was investigated in sweet cherry to facilitate breeding improvement for fruit quality. The fruits of five sweet cherry populations (N = 372), three F1 and two F2, were sampled over two years to evaluate SSC, TA, and the content of individual sugars (glucose, fructose, sorbitol, and sucrose) and organic acids (malic, quinic, oxalic, citric, and shikimic) by ultra-performance liquid chromatography. Glucose, followed by fructose, was the most abundant sugar, while malic acid was the predominant acid. Sorbitol and malic acid were the most stable compounds between years, and had the highest heritability, being also the best correlated to SSC and TA, respectively, revealing their relevance for breeding. Significantly positive correlations were observed among sugars and SSC, and acids and TA, but high interannual variability between years was observed for all traits. Quantitative trait loci (QTL) mapping for SSC, sugars, TA, and organic acids was performed using a multi-family approach with FlexQTL™. Twenty QTLs were detected consistently during the two phenotyped years, and several relevant regions with overlapping QTLs for sugars and acids were also identified. The results confirmed major stable SSC and TA QTLs on the linkage groups 4 and 6, respectively. Within the main LG4 SSC QTL region, where maturity and fruit development time QTLs have been previously detected, three stable sugar (glucose, sorbitol, and sucrose) and two acid (quinic, shikimic) QTLs were also identified, suggesting a pleiotropic effect of ripening date on the content of these compounds. The major malic acid QTL overlapped with TA QTL on LG6; thus, TA QTL mapping on LG6 may correspond to malic acid QTLs. Haplotype analyses of major SSC and sugars QTL on LG4, and TA and malic acid on LG6 revealed haplotypes of breeding interest. Several candidate genes previously identified in other Prunus fruit species, like peach, were found to collocate with the QTLs detected herein. This work reports QTLs regions and haplotypes of sugar and acid content in a Prunus nonclimacteric stone fruit for the first time.