Dying-arm disease in grapevines: diagnosis of infection with Eutypa lata by metabolite analysis

Dying-arm disease in grapevines, produced by infection with the ascomycete Eutypa lata, is responsible for major production losses in vineyards. Dieback of the shoots and cordon is believed to be due to acetylenic phenol metabolites produced by the fungus. To identify specific metabolites that could potentially be used for diagnosis of infection, eight E. lata isolates were grown in vitro on hot water extracts from grape varieties with various degrees of tolerance to the foliar symptoms of E. lata dieback. HPLC analysis showed that eutypinol was consistently produced in large amounts, together with smaller amounts of methyleutypinol and eulatachromene; eutypine, the putative toxin, was produced solely on Sauvignon Blanc extract and then in only barely detectable amounts. When E. lata isolates from Cabernet Sauvignon and Merlot were grown on identical media, the amounts of metabolites produced differed significantly between isolates but the pattern of metabolites was quite similar, with eutypinol again predominating. The consistent production of eutypinol indicated that this was the most suitable metabolite for which to analyze in order to diagnose the presence of E. lata. Extraction and analysis of grapevine tissues exhibiting symptoms of dieback failed to show the presence of any metabolites. However, when infected cordon sections were placed in water and cultured for 5 days, eutypinol was readily detected in the aqueous solution; metabolites were not produced from uninfected tissue. This provides a method for detection of infected tissue and indicates that the toxic metabolites react at the point of production, disrupting the vascular structure and inhibiting transport of nutrients, rather than being translocated to tissues that exhibit symptoms.