Frontiers in the control of pathogenic fungi associated with the Esca disease complex

Doutoramento em Biologia - Instituto Superior de Agronomia / ULThe ‘esca disease complex’ is a term used to identify several syndromes associated with a fungal infection of the wood of Vitis vinifera L. or other Vitis species. The pathogenic agents induce the appearance of internal symptoms in the perennial organs, such as brown wood streaking, wood necrosis and wood decay; and they are believed to be indirectly involved in the manifestation of external symptoms in annual organs as well. Overall, an esca infection induces lower vigor, productivity, quality of the yield and sorter life span of affected plants. Despite several points regarding the etiology and epidemiology of this disease complex remain controversial, due to the recent increase in the disease’s reports and worldwide incidence, there is an urgent need to find effective control strategies both to prevent the spread of esca-associated pathogens and to treat infected vines. To tackle this issue, three strategies were investigated upon: biological control, endotherapy and foliar spray with selected fungicidesN/

The influence of the microstructural shape on the mechanical behaviour of interpenetrating phase composites

The microstructure-property relationship for interpenetrating phase composites (IPCs) is currently poorly understood. In an attempt to improve this understanding this study focused on one particular part of this relationship: the effect of phase shape on the elastic and plastic behaviour. A review of previous research showed that investigations had linked phase shape to the elastic and plastic behaviour of various inclusion reinforced composites, but that no similar work had been completed for IPCs. To study the complex response of the IPC microstructure under load, a numerical modelling analysis using the finite element method (FEM) was undertaken. Two three-dimensional models of IPCs were created, the first consisting of an interconnected spherical phase with the interstitial space forming the other interconnected phase, and the second replacing the spherical phase with an interconnected cylindrical phase. With the simulation of a uniaxial tension test under elastic and plastic conditions, these two models exhibited different responses based on the shape of the phases. Results from an analysis of the macroscopic behaviour identified that the cylindrical model produced greater effective properties than the spherical model at the same volume fraction. The influence of phase shape was connected to the increased contiguity of the superior phase within the IPC for the cylindrical model, which allowed similar levels of long-range continuity with smaller amounts of the superior phase (compared to the spherical model). An examination of microstructural stress distributions showed that preferential stress transfer occurred along paths of low compliance. This provided an explanation of how the improved contiguity of the stiffer (or stronger) phase could enhance the macroscopic effective properties of an IPC. Contiguity of the stronger phase was particularly important for plastic behaviour, where early yielding of the weaker phase requires the stronger phase to carry nearly all the load within itself

Understanding the control strategies effective against the esca leaf stripe symptom: the edge hypothesis

A peculiar symptom that may develop in grapevines affected by wood pathogens involved in the esca complex of diseases is the leaf stripe symptom, which also gives the name to the Grapevine Leaf Stripe Disease. Multiple studies have revealed strong links between fungal presence, wood symptomatology and expression of the leaf stripe symptom. However, numerous other factors have been shown to play roles in symptom onset, incidence, severity and yearly fluctuation of this disease. While the factors triggering the leaf stripe symptom are still under investigation, three control strategies have been proven effective for substantially reducing its expression, namely trunk surgery, and applications of sodium arsenite or a fertilizer mixture. These control strategies are examined here, including their (putative or confirmed) modes of action, and how they may influence the leaf stripe symptom development. In this article, we also propose the ‘edge’ hypothesis to tentatively explain symptoms onset, keeping in consideration past knowledge and recent advances in the understanding of the esca leaf stripe symptom. Ultimately, it is our intention to offer food-for-thought and and stimulate and stimulate debate within the phytopathological community

Understanding the control strategies effective against the esca leaf stripe symptom: the edge hypothesis

New and OpinionA peculiar symptom that may develop in grapevines affected by wood pathogens involved in the esca complex of diseases is the leaf stripe symptom, which also gives the name to the Grapevine Leaf Stripe Disease. Multiple studies have revealed strong links between fungal presence, wood symptomatology and expression of the leaf stripe symptom. However, numerous other factors have been shown to play roles in symptom onset, incidence, severity and yearly fluctuation of this disease. While the factors triggering the leaf stripe symptom are still under investigation, three control strategies have been proven effective for substantially reducing its expression, namely trunk surgery, and applications of sodium arsenite or a fertilizer mixture. These control strategies are examined here, including their (putative or confirmed) modes of action, and how they may influence the leaf stripe symptom development. In this article, we also propose the ‘edge’ hypothesis to tentatively explain symptoms onset, keeping in consideration past knowledge and recent advances in the understanding of the esca leaf stripe symptom. Ultimately, it is our intention to offer food-for-thought and stimulate debate within the phytopathological communityinfo:eu-repo/semantics/publishedVersio

White Rot Fungi (Hymenochaetales) and Esca of Grapevine: Insights from Recent Microbiome Studies

ReviewEsca is a major grapevine trunk disease that heavily affects vineyards in the Northern hemisphere. The etiology and epidemiology of this disease have been subject of dispute ever since the earliest disease reports. The reason behind such debate is the presence of multiple internal and external symptoms, as well as several putative and confirmed wood pathogens. While the role of pathogenic fungi, as causal agents of wood symptoms, has been thoroughly assessed, their role in the expression of leaf symptoms remains to be fully elucidated. In this review, we analyzed etiological and epidemiological data, with a special focus on the microbiological aspect of esca and the involvement of Hymenochaetales (Basidiomycota). Vineyard studies have associated leaf symptoms with the presence of white rot, most frequently caused by Fomitiporia mediterranea (Hymenochaetales), while tracheomycotic fungi are commonly found, with similar abundance, in symptomatic and asymptomatic vines. Pathogenicity trials have excluded a direct effect of Hymenochaetales species in triggering leaf symptoms, while the data concerning the role of tracheomycotic fungi remains controversial. Recent microbiome studies confirmed that F. mediterranea is more abundant in leafsymptomatic vines, and treatments that effectively control leaf symptoms, such as sodium arsenite spray and trunk surgery, act directly on the abundance of F. mediterranea or on the presence of white rot. This suggest that the simultaneous presence of Hymenochaetales and tracheomycotic fungi is a pre-requisite for leaf symptoms; however, the relation among fungal pathogens, grapevine and other biotic and abiotic factors needs further investigationinfo:eu-repo/semantics/publishedVersio

Fungicides and the grapevine wood mycobiome: a case study on Tracheomycotic Ascomycete Phaemoniella chlamydospora reveals potential for two novel control strategies

Original ResearchPhaeomoniella chlamydospora is a tracheomycotic fungus that colonizes the xylem of grapevines (Vitis vinifera L.), causing wood discoloration, brown wood streaking, gummosis, and wood necrosis, which negatively affect the overall health, productivity, and life span of vines. Current control strategies to prevent or cope with P. chlamydospora infections are frequently ineffective. Moreover, it is unclear how fungicides commonly applied in vineyards against downy and powdery mildew agents affect the wood mycobiome, including wood pathogens such as P. chlamydospora. In this study, we used next-generation sequencing to assess the effects of foliar spray of grapevines with inorganic (copper oxychloride and sulfur), synthetic (penconazole and fosetyl-aluminum), and natural (Blad) fungicides currently used against the downy and powdery mildews. The subjects of our investigation were (i) the resident wood mycobiome, (ii) the early colonization by a consortium of fungal wood endophytes (ACEA1), (iii) the wood colonization success of P. chlamydospora, and (iv) the in planta interaction between P. chlamydospora and ACEA1, under greenhouse conditions, in rooted grapevine cuttings of cv. Cabernet Sauvignon. The data obtained suggest that the resident mycobiome is affected by different fungicide treatments. In addition, the early colonization success of the endophytes composing ACEA1 varied in response to fungicides, with relative abundances of some taxa being overrepresented or underrepresented when compared with the control. The wood colonization by P. chlamydospora comported significant changes in the mycobiome composition, and in addition, it was greatly affected by the foliar spray with Blad, which decreased the relative abundance of this pathogen 12-fold (4.9%) when compared with the control (60.7%) and other treatments. The presence of the pathogen also decreased considerably when co-inoculated into the plant with ACEA1, reaching relative abundances between 13.9% and 2.0%, depending on the fungicide treatment applied. This study shows that fungicides sprayed to prevent infections of powdery and downy mildews have an control strategies to fight P. chlamydospora, namely, the foliar spray with Blad and the use of ACEA1. Further studies to confirm these results are requiredinfo:eu-repo/semantics/publishedVersio

Endotherapy of infected grapevine cuttings for the control of Phaeomoniella chlamydospora and Phaeoacremonium minimum

The pathogens Phaeomoniella chlamydospora and Phaeoacremonium minimum are associated with different syndromes of the esca disease complex affecting grapevine propagation material, and young and adult plants. Infections by these fungi occur in grapevine nurseries and in vineyards, with disease control strategies providing limited protection in both cases. Several chemicals are effective in vitro against these two pathogens, but treatment of infected plants, especially endotherapy, has not yet proven satisfactory. Five chemicals (elemental silver, fosetyl-Al, glutaraldehyde, hydrogen peroxide and Blad-containing oligomer) were tested in vitro, with the first four also tested in planta, by means of endotherapy, against Pa. chlamydospora and Pm. minimum. All chemicals were effective in vitro for preventing growth of both pathogens, at different concentrations. Endotherapy of rooted grapevine cuttings (cv. Touriga Nacional) was effective against Pa. chlamydospora for all the tested chemicals, with reductions in the frequency of re-isolation of this pathogen of 91–95% (glutaraldehyde), 68–96% (hydrogen peroxide), 68–77% (elemental silver) and 58–59% (fosetyl-Al) when compared with the water-treated experimental controls. The only treatment that was effective against Pm. minimum was glutaraldehyde, providing a 75–83% reduction in re-isolation frequency. These results indicate that endotherapy of young grapevines during early stages of infection may be an effective control strategy, especially against the wood pathogen Pa. chlamydospora.

Deposition Mechanism and Properties of Thin Polydopamine Films for High Added Value Applications in Surface Science at the Nanoscale

Polydopamine films have been introduced by Messersmith et al. as a possible “versatile” surface functionalization method allowing to coat the surface of almost all known materials even superhydrophobic surfaces. These new kinds of coatings also confer a plethora of functionalities to the coated materials owing to the complex chemistry of the catechol quinone moieties present on the surface of polydopamine. These coatings may hence become an interesting alternative to established surface coatings like self-assembled monolayers and polyelectrolyte multilayered films. In this review, we describe the knowledge acquired in the last 3 years about the deposition mechanisms of polydopamine films, their properties, and various applications in surface science at the nanoscale.Fonds Europeen de Developpement Economique et Regional (Chaptochem Project 2009-02-039-35