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Esca is a devastating wood-decay disease that affects major grape-producing areas around the world. Xylem pathogenic fungi produce a systemic effect on the development of foliar symptoms and glutathione metabolism in presence of oxidative species. This study focuses on sugar variations in Vitis vinifera leaves, in particular in early events occurring in esca. Biochemical, cytochemical and molecular methods showed that in esca-infected grapevines, photosynthetic pigment content did not vary significantly in leaves from apparently healthy canes (AC-AL), but decreased in leaves without symptoms on symptomatic canes (SC-AL). Starch grains were more abundant in AC-AL than in SC-AL containing wide plastoglobuli and numerous tannins. The starch level increased early, and then decreased with esca development. Fructose increased early by more than threefold, being the predominant soluble sugar in leaves with advanced esca symptoms. In response to damage induced by fungal infection, defence reactions such as fructose increased early and developed in esca leaves to scavenge reactive oxygen species and protect plant tissues. Esca infection leads to an early production of fructose involved in defence. [ABSTRACT FROM AUTHOR]