Diversity analysis of citrus fruit pulp acidity and sweetness: toward to understand the genetic cont

Acidity level is the main criteria of quality and physiological maturity evaluation for citrus fruit, especiallyfor mandarins and oranges. The acidity level varies during fruit development but also among species andvarieties, and also depends upon rootstock and environmental factors such as temperature and rainfall. Acidmetabolism is linked to sugar metabolism. To better control fruit maturity and harvest time, it is necessaryto understand the genetic control and the parameters influencing the variation of acidity and sweetness. Citrus diversity was investigated by selecting 87 varieties belonging to the 8 major Citrus species grownunder the same environmental and cultivation conditions. The juice acidity and sweetness were analysedby assessing pH Na-neutralization and by refraction index, respectively, and their components by HPLC. The sequence polymorphisms of 9 candidate genes encoding for key enzymes of sugars and organic acidsmetabolic pathways were investigated by SSCP (Single Strand Conformation Polymorphism). Whatever thebiochemical or molecular analysis, the observed structure of the Citrus diversity was organized around theancestral species (mandarin, pummelo and citron). As expected, the secondary species were closely relatedto their putative species progenitors. The biochemical diversity was strongly correlated to molecular SSCPdiversity without having any certainty on the cause and effect relationship.