Chemical and Spectroscopic Characteristics of the Wood of Vitis vinifera Cv. Sangiovese Affected by Esca Disease

Chemical and spectroscopic analyses (13C cross-polarization-magic angle spinning NMR and attenuated total reflection Fourier transform infrared spectroscopies) were carried out on the wood of Vitis vinifera cv. Sangiovese with brown-red discoloration and black streaks caused by esca disease. The analyses of the brown-red wood revealed the destruction of hemicelluloses and noncrystalline cellulose as well as modifications in the pectic and ligninic wood fractions. The pectic fraction consisted of carbohydrates associated with polyphenols. The lignin fraction exhibited only a few changes in the aromatic systems and a partial demethylation, and it appeared to be associated with condensed phenolic components probably arising from response polyphenols. The degradation of hemicelluloses and noncrystalline cellulose in brown-red wood, where the pathogens Phaeoacremonium aleophilum and Phaeomoniella chlamydospora prevail with respect to the other fungus Fomitiporia mediterranea, was consistent with reports on the degradative activity of such fungi in vitro carried out on model substrates. The observed alterations could also be attributed to the radical oxidation process caused by the oxidative response of defense itself triggered by infection, as suggested by the accumulation of postinfectional compounds. The analyses of wood tissue with black streaks showed less marked deterioration; here, an increase in pectic and phenolic substances, which probably accumulate in the xylem vessels as a response to the infection, was observed.