Rootstock Effects on Anthocyanin Accumulation and Associated Biosynthetic Gene Expression and Enzyme Activity during Fruit Development and Ripening of Blood Oranges

Blood orange ( Citrus sinensis L. Osbeck) is a rare commercial citrus fruit containing abundant anthocyanins and has numerous health benefits. Blood orange rootstock determines the fruit yield and quality. This study evaluated the effect of the three most commonly used rootstocks on the fruit features, color index, physicochemical parameters, anthocyanin accumulation, the anthocyanin biosynthetic gene expression, and the associated enzymes during the fruit development and ripening of ‘Tarocco’ blood orange. The highest anthocyanin content at harvest was found in blood orange trees grafted onto ‘Trifoliate orange’ ( Poncirus trifoliata L. Raf., Pt ) rootstock. Molecular analyses revealed that the rootstock affects the anthocyanin accumulation in the blood orange. Additionally, there was a strong correlation between the anthocyanin content and the expression and the activity of related genes and enzymes, respectively. Based on gene expression and enzymatic activity analyses, Pt rootstock promotes a very high anthocyanin accumulation in ‘Tarocco’ blood orange fruit. Accordingly, Pt is the promising rootstock for producing good quality and highly nutritious ‘Tarocco’ blood orange fruit for commercial purposes.