Developing effective physiological strategies to rejuvenate virus-infected vineyards by lowering the virus load in infected grapevines

Abstract

Context and purpose of the study. The wine industries face significant challenges from two highly detrimental viruses: leafroll and red blotch. These viruses pose a serious threat to grape production on a global scale, and currently, there are no effective treatment options available. The most reliable method for managing this issue is to remove infected vines and replace them with certified stock that has been thoroughly tested for virus contamination. This study evaluates phloem girdling as a strategy to reduce virus load in leafroll-infected grapevines, aiming to enhance their health and productivity.

Material and methods. Girdling involves making precise cuts in the phloem. It was performed on canes before veraison, targeting specific regions between the proximal and distal clusters of healthy and infected mature Cabernet Sauvignon vines trained onto the VSP system. Commercial laboratories employing molecular techniques measured the virus concentration and various metabolites in the healthy and infected vines before and after girdling.

Results. The vines responded favorably to this approach, creating calluses that sealed the incisions. A compelling outcome of this process was observed in the leaves above the girdled areas, which displayed a striking red color due to anthocyanin accumulation caused by sugars being trapped in the leaves. This reddening is distinctly different from the typical symptoms of leafroll infection, where the entire leaf turns red while areas near the main veins remain green, creating a recognizable visual effect. Furthermore, the study revealed a substantial reduction in virus load within the girdled canes as compared to ungirdled ones. Additionally, it assessed various vital primary metabolites, including sugars, organic acids, and nitrogen compounds, as well as secondary metabolites such as flavanols (tannins), flavonols, and anthocyanins, all crucial for high-quality winemaking. Remarkably, the levels of these metabolites showed minimal variation between clusters of girdled and ungirdled shoots, indicating that girdling does not negatively impact the overall health of the vines. In summary, this study clearly demonstrates that phloem girdling, when consistently applied over multiple growing seasons, can effectively reduce virus loads in infected grapevines. This method provides a new way to deal with viral infections in vineyards and helps restore the health and productivity of the grapevines.