Plant-pathogen interactions within the esca disease complex

Abstract

This thesis presents an overview of the esca complex, a predominant grapevine trunk disease worldwide. Esca is one of the main causes of reduction of yield, plant decline and death of grapevines in most viticultural areas of the world. In recent years, research on esca has led to considerable progress in understanding the etiology, epidemiology and physiology of the disease and revealed its great complexity. This work covers the symptomatology in the trunk, leaves and berries, of each syndrome belonging to the esca complex and the characteristics of the different fungal species involved in the decline of the vine. Due to the effects of climate change, increasing attention is being paid to the impact that abiotic factors have on the development of plant diseases and on the mechanisms that can alter the relationship between pathogens and plants. Abiotic stresses, like drought or rainfall, can influence the tolerance or susceptibility of the plant to pathogens with consequences on plant-pathogen interactions, sometimes leading to a greater tendency to show symptoms, especially foliar ones. For this reason, this thesis compiles the available knowledge on the impact of host-pathogen-environment in the progress of the esca disease complex. To date, there is no certainty about the effects that abiotic factors have on plant-pathogen interaction but measurable evidences from several studies emphasize how they play a fundamental role in the definition of vine/pathogen interaction. Grapevines have developed a plethora of defence mechanisms to face pathogen attempts to attack and infect, which are activated as soon as they can detect their presence. Based on the available evidence we evaluated the ability of the plant to respond to biotic stresses through the production, locally or systematically, of defensive compounds derived from secondary metabolism, in particular phenolic compounds. Phytoalexins are the most prominent compounds that accumulate at the site of infection, reaching toxic concentrations for pathogens. Despite this, the role of phenolic compounds, including those that are synthesized constitutively, in the protection of plant against pathogens is not yet completely clear. The knowledge of plant-pathogen interaction can have useful implications in the determination of field infections and contribute to the development of new control strategies. In addition, if the plant’s innate defensive abilities could be stimulated, the use of fungicides could be reduced, along with the toxic effects for the environment, for man and for the plant.