Effect of esca-associated fungi on white and red grapevine cultivars

Togninia minima (Tmi), Phaeomoniella chlamydospora (Pch) and/or Fomitiporia mediterranea (Fme) are three well known esca-associated fungi. We compared two cultivars of Vitis vinifera, ‘Italia’ and ‘Sangiovese’ differing in susceptibility to these fungi. Scytalone, isosclerone, pullulan, and enzymes (laccase, tannase, peroxidase) produced by the pathogens, and host defence compounds (phenolics) were used for the comparison. The fungal metabolites were found in bioactive concentrations in leaves, rachises and berries of esca-affected vines at various stages of growth. The findings suggest that at least a part of esca foliar and fruit symptoms are caused by toxic fungal metabolites originating in the infected tissues and translocated to the crown via the xylem stream. Absorption of weak solutions of the fungal metabolites by sound leaves and berries of both cvs. induced esca-like symptoms. The presence of laccase, tannase and phenoloxidase in infected tissues aided symptom development. The concentration of constitutive or inducible phenolics in both cvs. varied in relation to phenological phases. Values of almost all the parameters measured in this study indicated that grapevines infected with Tmi and Pch gave a different response than vines infected by Tmi, Pch and Fme. These results indicate that infection by all three fungi gives rise to a range of biochemical and physiological events leading to the full scale of esca symptoms.