Confronting leafroll disease amid climate change – potential strategies for a resilient future

Abstract

Climate change is presenting significant challenges for grape production, notably by increasing the severity and spread of grapevine leafroll disease (GLD). Warmer temperatures foster environments that are more favorable to insect vectors, which can ultimately threaten wine quality and alter traditional terroir. The rising temperatures experienced during winters and summers are leading to larger populations of these vectors (mealybugs), thereby accelerating viral transmission and affecting fruit maturity. This has resulted in lower yields, decreased sugar levels, and less coloration in the grapes. While there is currently no cure for GLD, there are proactive management strategies that can help mitigate its effects. These include removing infected vines, replanting with certified virus-free material, and employing insecticides to control vector populations. However, these methods can be labor-intensive and costly, leading to a search for more effective solutions. One promising approach involves enhancing the vines’ immune systems by targeting the virus load. A key focus of this study was to explore how girdling the phloem of infected vines at various growth stages can reduce this virus load. Girdling was performed on canes after veraison, applied to specific areas between the proximal and distal clusters. Remarkably, the vines responded positively to girdling; they formed calluses that bridged the girdled area, restoring vascular functionality. Additionally, the leaves above the girdled regions exhibited a striking red coloration due to the accumulation of anthocyanins, driven by sugars that were confined to the leaves. This response is notably different from the typical reddening seen in GLD-infected vines, where the coloration is uneven and leaves a distinct green vein pattern. Importantly, the study found that girdled canes demonstrated a lower concentration of the virus compared to their ungirdled counterparts. Furthermore, essential primary metabolites, such as sugars, acids, and nitrogenous compounds, as well as valuable secondary metabolites, like flavanols (tannins), flavonols, and anthocyanins, crucial for winemaking, remained largely consistent between girdled and ungirdled shoots. In conclusion, this research provides valuable insights into how phloem girdling can be an effective strategy for reducing the virus load in infected vines, leading to restored vine health and improved grape quality. Such innovative practices could be instrumental in ensuring the sustainability of grape production in the face of climate change.

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