Abstract
Esca 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 leaf-symptomatic 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 investigation.
Highlights
Since the early 2000 s, extensive scientific research has deepened our understanding of the leaf symptoms associated with the esca disease in grapevine
Under current classification [9], esca symptoms in leaves, known as tiger stripes, occur in vines affected by grapevine leaf stripe disease (GLSD) and esca proper, and they are known to be correlated to agronomical practices and other biotic and abiotic factors [10,11,12,13,14] (Figure 1A)
Elena et al [41] reported that Fomitiporia mediterranea (Fmed) was isolated exclusively from white rot or necrotic tissues of grapevines showing leaf symptoms, whereas P. chlamydospora (Pch) was isolated from both symptomatic and asymptomatic vines, and Phaeoacremonium minimum (Pmin) was more frequently isolated from asymptomatic ones
Summary
Since the early 2000 s, extensive scientific research has deepened our understanding of the leaf symptoms associated with the esca disease in grapevine. Details over the past and modern views of esca and leaf symptoms were examined by several authors, including [6,9,13,19,20], while the involvement of white rot fungi (Hymenochaetales) in grapevine trunk diseases has been reviewed by [21,22,23]. We will focus on the microbiological aspect of esca symptoms in leaves, in particular, on the role of white rot fungi, and we will examine both past knowledge and the main findings of these recent studies, discussing the implications over leaf symptoms’ etiology
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