Managing Esca in susceptible ‘Sauvignon blanc’ wine grapes through trunk renewal

Authors: Baumgartner, Kendra; LUNA, ISRAEL - University Of California, Davis; Rumbaugh, Arran

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2024
Publication Date: N/A
Citation: N/A
DOI: https://doi.org/10.1094/PHP-01-24-0011-SC

Interpretive Summary: The fungi that cause the grapevine trunk disease Esca reside in the wood, yet their toxic metabolites are detectable in symptomatic leaves and fruit. Trunk renewal was evaluated as a potential treatment for symptomatic vines in a 17-year-old, ‘Sauvignon blanc’ vineyard in Kelseyville, California. The canopy—and infected wood—were cut away and then a new canopy was retrained from a shoot off the presumably healthy wood at the base of the trunk. In September 2017, we mapped the locations of 97 symptomatic vines, which were distributed in a randomized complete block design within three experimental blocks. Immediately after pruning in February 2018, all 97 vines were cut off above the graft union. After five growing seasons, trunk renewal was successful, given that only one of 97 vines developed symptoms. Although a shoot did not grow from the base of 24% of the 97 vines, they were eliminated as sources of inoculum and thus the cost of replanting them was not wasted. Fruit was examined after five growing seasons, from four experimental treatments in the vineyard: asymptomatic (‘healthy’) fruit from healthy-retrained vines (RV-HF), healthy fruit from healthy vines not previously retrained (HV-HF), symptomatic fruit from symptomatic vines not previously retrained (SV-SF), and healthy fruit from symptomatic vines not previously retrained (SV-HF). A statistical analysis that compared concentrations of phenolic and volatile compounds grouped samples of SV-SF together and apart, with high concentrations of compounds that are associated with either a delay in ripening or induction of a host-response to Esca. SV-HF and HV-HF had normal concentrations of phenolic and volatile compounds, suggesting that the absence of fruit symptoms from vines with leaf symptoms can be used to drop/retain fruit clusters in a vineyard with Esca. RV-HF was characterized by unique chemical characteristics, suggesting that their young canopies were distinct from those of healthy vines that were not retrained.

Technical Abstract: The fungi that cause the grapevine trunk disease Esca reside in the wood, yet their toxic metabolites are detectable in symptomatic leaves and fruit. Trunk renewal was evaluated as a potential treatment for symptomatic vines in a 17-year-old, ‘Sauvignon blanc’ vineyard in Kelseyville, California. The canopy—and infected wood—were cut away and then a new canopy was retrained from a shoot off the presumably healthy wood at the base of the trunk. In September 2017, we mapped the locations of 97 symptomatic vines, which were distributed in a randomized complete block design within three experimental blocks. Immediately after pruning in February 2018, all 97 vines were cut off above the graft union. After five growing seasons, trunk renewal was successful, given that only one of 97 vines developed symptoms. Although a shoot did not grow from the base of 24% of the 97 vines, they were eliminated as sources of inoculum and thus the cost of replanting them was not wasted. Fruit was examined after five growing seasons, from four experimental treatments in the vineyard: asymptomatic (‘healthy’) fruit from healthy-retrained vines (RV-HF), healthy fruit from healthy vines not previously retrained (HV-HF), symptomatic fruit from symptomatic vines not previously retrained (SV-SF), and healthy fruit from symptomatic vines not previously retrained (SV-HF). Multifactor analysis of phenolic and volatile compounds grouped samples of SV-SF together and apart. SV-SF was associated with volatile compounds with green, grassy, or herbal aromas, and all the flavanol compounds in the phenolic profile, suggesting either a delay in ripening or induction of a host-response to infection. SV-HF and HV-HF shared high concentrations of tannins and terpenoids, indicating the normal ripening pattern of increasing terpenoid concentrations. RV-HF was characterized by the C6 aldehydes and alcohols, derived from the lipoxygenase pathway, suggesting a delay in ripening. Our finding that healthy fruit on vines with leaf symptoms shares similar phenolic and volatile profiles to healthy fruit on healthy vines suggests that the presence/absence of fruit symptoms can be used to drop/retain fruit clusters in a vineyard with Esca.