Fungal wood-degrading enzymes in esca-diseased grapevine and effects of carbohydrate environment on fungal development.

In esca disease affecting grapevines, Phaeomoniella chlamydospora and Phaeoacremonium minimum colonize the woody parts of the trunks and arms, where they obtain nutrition from xylem sap and, potentially, from residues resulting from the enzymatic breakdown of lignified cell walls, particularly osidic residues. We quantified the secretion of lignin peroxidase, manganese peroxidase and laccase by these fungi in woody tissues of selectively infected cuttings using immunolabeling and transmission electron microscopy. Our results indicated that the detection of these enzymes was generally higher in tissues infected with Phaeoacremonium minimum. These data were confirmed through immunodetection of enzymes secreted by hyphae of fungi grown in vitro. Additionally, we observed that the supply of various carbohydrates (mono, di, tri and tetrasaccharides and polymers) differentially influenced fungal growth and polypeptide secretion. Since some secreted polypeptides display detrimental effects on grapevine cells, these results raise the question of whether the carbohydrate environment could be a factor affecting the aggressiveness of these pathogens.