Investigation of contamination pathways of Esca-associated fungal pathogensand of fungicide-based control strategies
Abstract: Even though “Esca” may be as old as viticulture itself, new attention has been directedto this disease in recent years due to the dramatic increase in economic importance. A suddenwilting of Esca-affected grapevines, followed by the death of the entire plant, occurs in manygrapevine-growing areas of the world. Esca is a complex disease that comprises severalsymptoms caused by a set of fungal pathogens. Unfortunately, infected plants can often not becured, since foliar or wood treatments using fungicides do not lead to an effective control of therespective pathogens in the infested wood. Given the large number of wounds made topropagation material during the various nursery stages and also made as a result of repeatedpruning, hygiene and wound protection is of particular importance. Therefore, the effect ofvarious chemical and biological treatments on Esca-associated fungi, such as Phaeoacremoniumaleophilum (Pal), Phaeomoniella chlamydospora (Pch), and Fomitiporia mediterranea (Fmed),and on the disease progress of artificially infected plants was investigated in vitro and in field andgreenhouse experiments. For this purpose, several putative contamination pathways and differenttest systems have been evaluated to verify the ports of entry for fungal spores and the efficiencyof fungicides to control the disease.In the year 2009, vineyards of the DLR research station and of local grape growers wereinspected and the impact of Esca in these vineyards was evaluated. As published by otherauthors, the number of affected vines increased with their age. Furthermore, there are no cleardifferences in susceptibility and none of the varieties planted in the Palatinate showed anysuitable resistance. Plant material of diseased vines was collected and tested for the presence ofEsca-inducing pathogens. Mainly Phaeomoniella chlamydospora (Pch), Botryosphaeria species,Cylindrocarpon sp., Trichoderma sp. and mould fungi such as Alternaria sp. and Penicillium sp.were frequently found. All type of wounds created artificially represented suitable ports of entryfor all Esca-associated pathogens. Especially, infections with Cylindrocarpon destructanssignificantly reduced viability of the scions and had severe effects on plant growth as tested withinfected cuttings. Wound infections caused by polluted water that had been used to soakpropagation material led to a reduced growth of cions, especially when contaminated withCylindrocarpon spores.Growth tests in vitro showed that most fungicides tested exhibited antifungal capacities. TheTrichoderma-based product Trichostar® was an effective biological agent in the field, preventinginfection of wounds when applied one day before inoculation, whereas most fungicides were notable to sufficiently prevent colonisation of wounds by fungi.