Diagnosis of grapevine esca disease by immunological detection of Phaeomoniella chlamydospora.
Background and Aims: Esca is a devastating disease affecting grapevines all around the world induced by a complex of xylem-inhabiting fungi. Among them, Phaeomoniella chlamydospora has been considered as an early causal agent of the disease facilitating the access of opportunistic saprophytes whose mode of action should be further investigated. P. chlamydospora secreted into its culture medium a variety of polypeptides, the biochemical nature of which permitted us to develop a method of detection based on a serological test. Methods and Results: Polyclonal antibodies raised in rabbit against the polypeptide fraction recognised secreted fungal proteins in low amounts (commonly 1 ng). These antibodies showed a valuable specificity because they cross-reacted with polypeptides excreted by various strains of P. chlamydospora but not with those secreted by many other fungal pathogens commonly found in other grapevine infections. Importantly, as shown by the enzyme-linked immunosorbent assay test and immunolocalisation on ultrathin sections, they did not cross-react with the secreted polypeptides of various fungi intervening in other wood decay diseases, namely Eutypa dieback (Eutypa lata) and Black Dead Arm (Diplodia seriata and Neofusicoccum parvum). Using a serological approach, the presence of P. chlamydospora was detected in canes of selectively infected cuttings. Conclusions: The antibodies raised in rabbit against polypeptides secreted by P. chlamydospora are useful tools to specifically detect the presence of the pathogen. Significance of the Study: These results allow us to propose a reliable dot blot method to detect grapevine infection by P. chlamydospora. This method is non-destructive for grapevines, simple and rapid.