The Role of Low-Molecular Weight Fungal Metabolites in Eutypa Dieback Grapevine Trunk Disease (GTD)

This project focuses on the fundamental chemistries that GTD fungi causing Eutypa canker/dieback employ in infecting and causing damage to grapevines. We also are developing antioxidant/chelator (A/C) treatments for these GTD fungi which block their chemistries. Additionally, we are disseminating our findings on GTD causal systems and potential treatments to vineyard owners/managers and other parties. Our three Objectives for this two-year project are:

A) Understand the role of iron-binding compounds produced by the mixed-consortia fungi involved in Eutypa dieback, with particular focus on how these compounds generate hydroxyl radicals, the most damaging form of ‘free radical’ found in biological systems.

B) Use our enhanced understanding of Eutypa dieback to develop treatments and management strategies for the control of Eutypa GTD.

C) To disseminate and interpret our research results to vineyards personnel to allow a better practical understanding of how Eutypa dieback chemistries function in causing the disease, and disseminate results particularly related to treatments developed.

Findings to Date:
A New Causal Mechanism for Eutypa Dieback, which also has Potential for Involvement in Esca Disease: The three fungi in this study, Eutypa lata (Elata), Phaeomoniella chlamydospora (Pch), Phaeoacremonium minimum (Pmin) were all found to produce low molecular weight (LMW) polyphenolic compounds that reduce iron. Pch produced the greatest amount of polyphenolics and, in consortia growth with Pmin, also produced the greatest amount of iron reduction. The extracted LMW metabolites from these fungi were also found to nonenzymatically produce hydrogen peroxide. This previously unreported finding is important because hydrogen peroxide will react with reduced iron to generate highly destructive hydroxyl radicals. In other fungi, this type of chelator-mediated Fenton (CMF) reaction has been found to be responsible for aggressive damage and decay of plant tissue (wood cell walls). Our data provides the first evidence that Eutypa dieback, and also potentially esca disease, is not caused by enzymatic or toxin production by fungi. Rather, a CMF mechanism is active which causes both a canker and decay of grapevine wood. We postulate that as the canker/decay develops, fungal LMW metabolites may also diffuse to the foliage to produce end-stage scion/foliar symptoms. CMF mechanisms are known to be active in fungal attack of wood, causing common brown rot decay, but the mechanism has not previously been demonstrated to be causal in GTDs. Clear evidence for production of hydroxyl radicals suggests that CMF chemistry promoted by the pathogenic fungi is responsible for decay of the wood related to canker production in Eutypa dieback.

Development of Potential Treatments for Eutypa/Esca Based on Knowledge of New CMF Disease Mechanism: Laboratory testing of both A/Cs and biocontrol agents continues. However, one of the A/Cs (butylated hydroxyanisole or BHA) is a low-cost, food-safe antioxidant that shows suitability for potential treatments. BHA is showing positive results in completely preventing growth of all three fungal pathogens at relatively low concentrations (≥ 0.5 mM). We will continue testing and, although not part of AVF funded research, plan to conduct limited testing of BHA in pathogen-inoculated grapes in summer.