Phenolic Compounds Have a Role in the Defence Mechanism Protecting Grapevine against the Fungi Involved in Petri Disease

Abstract

Scanning electron microscopy of stems and roots of vine plants affected by Petri disease demonstrated that the obstruction of xylem vessels and reduction in the flow of xylem sap, two symptoms of this disease, were mainly caused by tyloses forming in the vessels, and, to a lesser extent, by the accumulation of aggregates. Fungal hyphae were also found in the xylem. These hyphae propagated via the xylem and invaded other vessels or adjacent parenchymatic cells through the pit. Analysis of lignin peroxidase, manganese peroxidase and laccase activity (all of which are involved in lignin degradation) in different fungi isolated from Petri-disease-infected grapevines found that Phaeoacremonium aleophilum expressed low specific activity for manganese peroxidase and high specific activity for both lignin peroxidase and laccase, while Phaeomoniella chlamydospora showed no activity for any of these enzymes. All these enzyme activities were inhibited by the phenolic compounds in grapevine: p-coumaric acid, catechin, caffeic acid and tannins. The phenolic compounds also had a direct effect on fungal growth and sporulation. When SO4 vines affected by Petri disease were treated with Brotomax (a product that stimulates synthesis of phenolic compounds) plants showed an increase in growth and a reduction in Petri-disease symptoms. Any new shoots and roots formed after Brotomax treatment did not show any sign of obstruction or tyloses formation.