2009). An example from zoology is the study by Zuluaga-Montero et al. (2010), focusing on sea fans (Gorgonia ventalina), in which the results indicated Vactosertib cell line that the fungal community composition did

not differ significantly between healthy and diseased tissues in each reef and that the differences in fungal communities were more attributable to differences between reefs than to the health of the studied colonies. Defining a fungus as a pathogen implies a difference in its incidence and certainly in its PF-02341066 clinical trial abundance between healthy and diseased individuals. The appearance of the disease symptoms should be the consequence of the increasing proliferation of the causal pathogen and this should have an impact on the fungal community structure. In the case of esca, such a shift in fungal community structure is not observed. In our study, however, a single fungal OTU (based on ITS similarity) possibly embraces very closely related species, subspecies or strains that have a different virulence

and could be differentially associated with healthy or diseased plants, as for instance in the case of Alternaria (Table 1, Pryor and Michailides 2002), Phaeomoniella chlamydospora (Mostert et al. 2006) or Phaeoacremonium angustius (Santos et al. 2005). SYN-117 purchase Also, cumulated small differences in abundance of several OTUs might eventually differentiate between healthy and diseased plants, but such slight differences in abundance are, each taken separately, too small to contribute to a significant distinction between healthy and diseased plants in a PCA analysis (Fig. 6). Nevertheless, our experiment was conducted

in a single, small vineyard plot, making it unlikely to observe differences in virulence between strains or subspecies associated with adjacent plants. If some strains were indeed more virulent within a single OTU, this would have resulted in an increase of the abundance of such an OTU in diseased grapevine plants, as a more virulent strain is expected to be more invasive than less virulent ones. Neither is it likely that unculturable fungi are responsible for the emergence of esca in the sense that a shift toward pathogenicity – and consequently invasiveness – of these fungi Rebamipide should also have an impact on the culturable part of the fungal community associated with grapevine, which is not the case in our study. Nevertheless, there remains an urgent need to characterize the genotypes of the fungi associated with esca disease in more detail before we can firmly exclude fungi as the principal cause of esca. Other organisms, such as bacteria, may be involved in esca but eventual differences between the bacterial communities associated with diseased or healthy grapevines have never been studied. As suggested by Bertsch et al.