Influence of the rootstock and the environment on qualitative traits and phenolic composition in blood oranges

Citrus fruits, and particularly blood oranges, are rich in phenolic compounds that affect peel and juice colour, sensory, and nutraceutical properties thus providing relevant health benefits. Polyphenol content in blood oranges is remarkably influenced by genetic and environmental factors such as climate and soil conditions, as well as agronomic practices, including the adopted rootstock. In this context, the aim of the research, conducted for two consecutive years, was to study i) the influence of ten different rootstocks, and ii) the effect of winter minimum temperatures on polyphenol accumulation in 'Tarocco Scire' blood orange fruits. The rootstocks under study were 'Bitters', 'Carpenter' and 'Furr' citrandarins (hybrids of Sunki mandarin x 'Swingle' trifoliate orange, released by the University of California, Riverside, in 2009), 'F6P12 (R)' and 'F6P13' (hybrids of Citrus latipes and Poncirus trifoliata released by CREA-OFA, Italy, in 2014), 'Troyer', 'Carrizo' and 'C35' citranges, 'Swingle' citrumelo, and 'Severinia' [Severinia buxifolia (Poir.) Ten.]. Chromatographic analyses allowed the identification and quantification of 24 phenolic compounds (6 anthocyanins, 5 flavanones, 1 flavone and 12 hydroxycinnamic acids). All these metabolites, especially anthocyanins, were most accumulated in the fruits in all the rootstocks for the year characterized by particularly low temperatures during fruit ripening. The results showed significant differences among biochemical subclasses and in individual phenolic compounds and highlighted a significant effect of both rootstock and environment (and their interaction) on the metabolic profile of the juice.